Why Did My Fish Die So Fast? (Top Beginner Fish Keeping Mistakes to Avoid)

Keeping fish in an aquarium is fun, and it is one of the most popular hobbies among pet keepers around the world. Sadly, the truth is that on the average fish only live for 3 weeks after left the shops. What can cause the fish die so quickly?

In at least over 90% cases, fish die early because of the following common beginners’ mistakes:
1. The fish owner used tap water without using an aquarium water conditioner.
2. Shock from sudden change in water temperature, and/or water chemistry (or no heater at all for tropical fish).
3. Ammonia and/or nitrite poisoning. (or no aquarium filter at all)

For Reason #1 – Fish Died to Untreated Tap Water

You must know that fish can’t survive in untreated tap water. Tap water contains chlorine and chloramines. While Chlorine is able to evaporate slowly if you let the tap water sit for a few days, chloramines is a different story and it is there to stay. Both chlorine and chloramine can and will kill the fish.

The solution to this problem is very simple. Buy a bottle of aquarium water conditioner. Years ago when I was a kid, people used solid crystal like water conditioner. Nowadays, more water conditioners are in liquid form.

I have personally used Seachem Prime, Kordon NovAqua+, Tetra AquaSafe, and Hikari Ultimate.

While they are all good and work just fine, I recommend Prime for new tanks because it can not only do the typical tasks of water conditioner which is to neutralize chlorine and chloramine, but it can also detoxify ammonia and nitrite for up to 48 hours, which can come in handy for a new tank.

For Reason #2 – Fish Died to Shock From Sudden Changes

Most fish can adapt to a certain range of water chemistry (PH, hardness, etc.) and water temperature without problem if given time. However, many new fish keepers do not know this. They will simply “dump” newly bought fish into their fish tanks immediately. The water in the tank obviously has different chemistry makeup and temperature compared with the water in the plastic bag that came with the fish. Unlike human being, fish are cold blood animal, and they can’t regulate their own body temperature like we do. Sudden change of water temperature can “shock” the fish and even cause them to die! The water PH and hardness are also extremely important; the sudden drastic change in either of them can cause fish to die.

Solution: Before you open the plastic bag, put the bag into the fish tank water. Let it sit there for at least 20 minutes for the temperature of the water in the plastic bag to become the same as the water in the tank. Many novice fish keepers do that after listening to the sellers at the fish stores, however, what they miss is the next step.

Now the water temperature is the same after the fish bag has been sitting in the fish tank water for over 20 minutes, but the water chemistry such as PH and hardness are still different! What now?

This is what I usually do. Use a plastic fish container (the little plastic box the fish store salesmen use to keep the fish caught from the tanks before putting them into a plastic bag), and dump the fish & water from the plastic bag into the container. There is no need to transfer all the water if the container is not big enough. Then get rid of some water from the container (throw that water away, do not put it into the fish tank), and refill the container with water from the tank.

Wait for 10~15 minutes, then get rid of some more water from the container, and refill it with the water from the fish tank. Repeat that process every 10~15 minutes with no more than 25~30% of water replaced each time…until the water in the container is mostly from the fish tank instead of the original water from the plastic bag. In this way, the fish have the time to slowly get used to the new water chemistry. The whole acclimating process usually takes me about 1.5 hours. For more sensitive fish, it can take 2~3 hours before I feel safe to add the fish into the tank.

We based the above scenario on the assumption that you have a heater if the fish you keep are tropical. It does not matter how slowly you try to make the fish to adapt to the new temperature, tropical fish (such as betta) will die if there is no heater to keep the water at the tropical water temperature which is usually around mid 72~80F+.
If you are looking for a heater, I would recommend Rena SmartHeater. I use a 50w heater in a 40-gallon tank, and the temperature is very stable since I have good water flow around it.

For Reason #3 – Fish Died to Ammonia and Nitrite Poisoning

Ammonia and nitrite poisoning is a more complex problem. First, you MUST have a filter running 24/7 if you plan to have fish. Without a filter, no fish will be alive for long. That is certain and there is no way to get around it. If you are looking for advice on a filter, I recommend AquaClear power filter for small size fish tanks of up to 30 gallons. They are very reliable.

For medium to large sized tanks, I recommend canister filters. They are more efficient at biological filtration, and they make no noise at all, but they cost more.

I personally use an EHEIM Classic 2213 for my 40-gallon tank, and I am very happy with it. It is a high quality German brand.

Now let us talk about why we need a filter and why there is ammonia and nitrite poisoning. Fish produce ammonia as a natural waste. Ammonia is toxic and it will harm the fish.

In a natural environment such as a lake or a river, there is so much water and it removes ammonia quickly, but in a closed system such as in a fish tank, ammonia builds up and become more and more concentrated quickly! It burns the fish’s gills, and it can kill the fish when the concentration is too high or exposed to low concentration for too long. Usually in two to three weeks, the level of ammonia concentration in a fish tank will be sufficient to kill the fish.

Now what? How do we remove the ammonia from an aquarium?

The answer is you do not need to physically remove it. In a well established aquarium, there are enough naturally occurring bacteria that feed on ammonia as food. Most of these bacteria live on the filter media where there are lots of surface areas. (These bacteria only colonize in the surface areas)! The ammonia feeding bacteria will convert ammonia to nitrite. However, nitrite is even more toxic than ammonia!

Now what? There is a different type of bacteria feeding on nitrite, and convert it into a much less harmful form – nitrate. The second type of bacteria also colonizes the surface areas in the fish tank, and just like the first type of bacteria, they mostly stay on the filter media because that is where the most surface areas are in a fish tank.

Nitrate is completely harmless to the fish until there is extremely high concentration, while ammonia and nitrite must be kept at 0 at all times, if you want your fish to live.

However, it takes up to 6~8 weeks for these two types of bacteria to grow into sufficient number in order to keep the ammonia and nitrite at 0, if…and only if there is a constant source of ammonia. By having fish in the aquarium, there is a constant source of ammonia, but the fish will usually die before the 6~8 weeks is up!

What did I say? You will never have remotely close to enough bacteria to feed on ammonia and nitrite if there is no fish (source of ammonia). But your fish will also die if you add it into the fish tank before there is enough bacteria. It makes no sense, does it? It surely sounds like nobody can keep fish alive at all if the fish tank is newly set up.

It actually makes perfect sense.

Solution to the #3 problem?  You should not add any fish into a new aquarium until you do a fishless nitrogen cycle!

To test your water chemistry for ammonia, nitrite, nitrate, and PH, you need a liquid water test kit. (Paper strip kits are not accurate at all.)
I use API freshwater master kit.

For saltwater aquariums, you need a different test kit called API Saltwater master kit.

For detailed information on nitrogen cycle, please read Fishless Nitrogen Cycling.

Lets hope more novice fish keepers do things right, so there will be fewer fish die in home aquariums.

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122 thoughts on “Why Did My Fish Die So Fast? (Top Beginner Fish Keeping Mistakes to Avoid)

    • Over a year is definitely not enough for most fish species. Most fish can live for much longer than just a year. Depend on the actual fish species, the typical aquarium fish’s life span is anywhere from 2~10 years. Some of them can live much longer. If only sometimes your fish live over a year, then there is definitely room for improvement.

  1. Ive had my fish for ten years got a bigger tank put some of their old water and new water.i have done this many times. Today i did the same and they all died. They were so big n beautiful im just heart broken!

    • Maybe there is too much new water? If the water hardness and PH had changed too much, the fish would not be able to adapt and it might cause them to die.
      Whenever you do water change or tank transfer, it is the best to keep at least 50% of old water. The fish should be given time to adapt…instead of just dump them in.

    • You have to be more specific about your situation. Please come to our forum to give more detailed information such as your tank size, filter type, how long have you had your fish, how often and how much do you feed them etc. Without any information we can’t answer your question.

        • If you looked at the previous posts, he/she/or maybe you have asked why did your fish die. Without further information on what you have, and what you have done so far, there is no way to pinpoint the specific cause. I did ask for some more information in details in order to answer the question. The “further information” he/she/you replied was “I got girl and boy fishes”. That was indeed not helping to fill me in on the situation.

  2. I have had a well established 100 litre tank for nearly a year. It’s beautiful. Until today. Last week well 6 days to be accurate I Brought a nee fish to join my panda moor and black moor.I choose a pearl fin gold fish *the puffy looking ones as advised by the pet store. However today he was bobbing about the top at first I suspected swim bladder but within an hour he was dead. Tested waster with a liquid testing kit and levels were OK. Did a 40% water change after removing him and retested a little while later still all OK. So why did he die?

    • Perhaps the new fish was not able to adapt to the new water in your aquarium. The introduction of new fish is one of the hardest part. If the fish can adapt, they live. If not, they often get sick or die.

  3. I had a shrimp in my fish tank for over a year. I changed the water in the tank several times. The shrimp developed bumps on the back and died. Any ideas why it died?

    • Sorry, there can be many reasons for the shrimp to die. I am unsure of the actual cause without a lot of details such as fish tank size, the filter you use, heater you use, the food, and the actual species of your shrimp. How often do you change the water, what water conditioner do you use, etc.

  4. I brought new fish tank stones and 6 fishes starting 2 day my fishes are good i give them 1 time food in a day but my 2 fish die early morning after that i think reason will be food is not sufficient for theme then i give them food 3 times in a day after five day 1 more fish at evening day im change water every 4-5 days

    • Hi,
      You only need to feed your fish once a day. Feed them no more than what they can finish (all of it) within a minute. Overfeeding is one of the most common problems in fish keeping and contribute to a lot of fish deaths.

  5. Only now do I know what were all the reasons behind my fish sudden death everything I bring new ones. Thanks to the admin for the detailed analysis of the problem. Got a question here. How should we feed our fish. Can there be any variety or it should only be the same packaged food we were given during our purchase.?

    • Hi Naveen,
      Thank you for reading the article.
      It is the best to get some high quality fish food. We also have articles about fish food on our blog. You may check them out to find your answer. If you still have questions, feel free to ask them on our forum. 😉

  6. I have had my guppy and platy fish in my pond(which also has a water Lilly) for nearly 11years and they multiplied really fast. But when I put new goldfishes in it (25 or sthg, my cousin bought me), both the goldfish(in gps of 7) and guppy and platy are dying after 3/4days… Pls tell me why… can’t bear to lose more…😞

    • Hi Jane,
      How big is your pond? Do you have a filter system running 24/7?
      Goldfish are known for their messy eating/pooping habits and the large amount of ammonia they can produce. It is very likely the newly added goldfish have overstocked the pond. It is causing an ammonia spike, which will eventually kill all fish if it is not fixed.

  7. It’s an average pond and no I don’t have a filter system… now there’s only some 5/6 gold fish in it (rest died)… will that help?? Or should I remove the goldfish??

    • Without a filter system, ammonia will build up and eventually kill all fish.
      You first need to figure it out how big your pond is, then get a filter system for it accordingly. Please check out our article on Aquarium Filters to see why you need it. No fish can be kept alive without a filter. Unless your pond is huge with tons of aquatic plants while having only a few fish.

      • You don’t necessarily need a filter for an outdoor pond, as long as you do a water change regularly and have a few live plants. We have raised fish for years in many outdoor ponds from 150 gallons to 500 gallons and never used a filter. These fish have been living long health lives without fail or a filter. However, I will say that adding a filter does improve the water clarity if you’d like to see the fish even when they’re deep below the surface.

        • If you have enough plants and algae to the point they will absorb all the ammonia produced by the fish, then surely you do not need a filter. In most cases, we do not know the “break even” point for ammonia. It is safer to use a filter system.

  8. Hi admin,
    I had 4 Gold fish 2 tiger fish and 2 big shark fish they were about 2 weeks then the started dying any reason why they died and after my Gold fish started dying my shark fish were eating them.

    • Too small of fish tank perhaps? What filter system are you using?
      “Tiger fish” can be many different fish species. I need the exactly fish species to be sure. Same goes for “big shark fish”. They might not even belong in the same fish tank since their natural habitat are different.

  9. I have a new tank . Set it up 4 about wk b 4 buying my fish. I have a tank heater , checked everything , the PH , alkinity, chlorine, ammonia & all b 4 I bought my fish. I bought 2 tiger barbs , 2 clown loaches , 2 angles , 2 sharks and 1 sucker. Brought them home let the bag sit in the water 4 -2 hrs then put them in the Tank. 3days later my sucker fish was dead.
    The next week we went and got another sucker fish and 3 dalmatian mollies. Did the same with the bags. Did not add their water to my tank tho. We noticed that one of my clown loaches had ick . We treated the tank , both my clown loaches died that day . Then the next day 1 of my shark fish was dead and my sucker that I had for 2 days was dead . I cheked all my levels and every thing was spot on . Would you know why they all died at once. I had already put my filter back in and took out 25% of water and treated it b 4 adding new water to tank after ick treatment. Plz help me . I love fish and fish Tanks. This is my first attempt at owning one and I really don’t want to give up. Thank you for all the help you could give me .

    • Maybe the treatment you used was too harsh on the fish? Treating ick can be done without using medications. Check out our article on ick.

  10. We have all kinds of fish. But we get new ones, and we float them, then the water thing, guess what the new ones die. The water is conditioned. The others dont die and they was new once upon a time. So what now!

    • Did you acclimate the new fish well? They need more than just the same water temperature. Other factors such as water PH, hardness, and even nitrate concentration can affect fish if it changes all the sudden. You need to add fish tank water into the new fish container little by little until it is almost all fish tank water in the container. Fish need time to adapt.

    • Hi,
      Many things could have gone wrong.

      We need more information to pin point it. Such as the actual tank size. The fish species. What water conditioner did you use. What filter do you have.

  11. i have a flat fish tank outdoor my house with a capacity of 1000 litres. i have put around 120 pet fishes (the gold, gold with black shades, black and white pet sharks). Everyday one or the other fish die wen i see in the morning. I add additional water to the tank if the level is below the normal. Can u plz help to my fish sustain in the tank.

    • Do you have a filter system in your fish tank? If so, what filter is it?
      Are you using an aquarium water conditioner? If so, what is it?
      Have you added water conditioner to the new water and let it sit to have the same temperature before adding it to the fish tank?

  12. I had two black moore fish in my tank which were perfectly fine until a couple of day back.I did my usual (50%) water change and my black moore suddenly started to fli-over and both of them died.
    I have been using the same water source. This is a fairly new tank.Approximately around a couple of months old.

    Tank Capacity: 40 Liters.

    2 – Fancy Gold
    2- White Gold
    4- Bala Shark
    2- Small Koi Carp

    • Maybe you did not acclimate them well during the water change? You can easily shock and kill your fish if the temperature, PH, hardness, etc. of the new water is too different from the old water from the tank.

  13. I had 16 fishes in my tank and now I have just 10 remaining. The fishes are having a white border on their gills and fins I don’t have a filter system ..i donno how it happened overnight..can you explain the reason?!

    • How big is your fish tank? It is likely you are overstocking your fish tank.
      Then you have mentioned “no filter system”. That is a big no in fish keeping. No aquarium filter = no way to keep fish alive for long.

  14. I have a 29 gallon fish tank went to pet smart had my water tested they said it was great I even let it sit for 1 week like they told me to bought 10 tropical fish and 1 alg eater did what they told me to.After 1 day one died after 3 days another one after 1 week one more and last night my alg eater was dead I got 5 more left.what can I do for the rest to survive.

    • These chain pet stores never give the right advice. Their employees are simply not trained to answer professional questions about pet care.
      If you read the article of “Aquarium Nitrogen Cycle and fishless Cycling”, you should know the reasons.

      Let the fish tank “sit” will do nothing.

  15. Hi!
    I have recently bought a fish tank
    My fish all have died in a week or two until recently I bought new fishes and they seem to be doing pretty well! Your article helped a lot. Its been 3 weeks All still happy and active. I just need tips to make sure they survive Should I do very partial water changes or complete water changes? I also have guppies in a fish bowl Tips for them? My fish tank is 30 gallons. Anyway thanks after all

    • Hi Faris Ahmad,
      Never do 100% water change. Fish will get into shock and die easily if you do that. They do not like large swings in their environment. Stick with 30~50% partial water change weekly. Make sure your filter system and heater are running properly.

    • Hi chanula,
      There is not enough information for me to find out the cause for your loss.
      You need to tell me more details first. 🙂

  16. Okay, I realise I may be doing the new hobbyist obsessive thing (which has brought me to this thread!) but I’ve got my first aquarium fish today (cardinal tetras) and for like 15 seconds or something I failed to realise that one was left in the bag after I released them. Now, I won’t ever release them the same way again (I’ll lower the bag so they have to swim up and out) so that’s a lesson learned, and I did the water temp/ph thing but I’m so worried that I might have stressed or harmed this little fish. He’s swimming along with his buddies now and looks perfectly okay but I feel terrible. 🙁

    • Hi Elle,
      If the fish is fine, then there is no need to worry about it. The fish will act weird almost immediately if they are in shock. Otherwise, they are most likely fine.

  17. i have 5 fishes and one of them died this morning i dont know how but she was not eating anything and whenever i gave her food other fish ate all food. can you tell me how to give them food and what must be the reason behind her death

    • hi abhishek,
      How long have you had your fish? Size of the fish tank? What filter system and heater? What exactly fish species are they?
      I need more information to try to find out what’s wrong.

  18. Thanks for the great information here. I followed the steps between you, the pet store and the pamphlet. I have a 20 gallon tank, it’s been cycled and I have existing fish who have been around for several years and almost entirely bottom feeders. Yesterday I introduced 3 guppies and 4 tetras. One guppy died overnight, 3 tetras died this afternoon (although 1 was eaten by the filter so doesn’t count) and I think another guppy is on the way out. I let the water acclimate about 40 mins for temp, and swapped in new tank water for about another 40 min. All of my existing fish and fine and we’re not abusing the others. (All community fish, tank 78-79° F) Any suggestions?

    • Hello Erin,
      Did you also acclimate the fish with the tank water when you introduce them to your aquarium? The temperature is only one of the things they must get used to before being released into the fish tank.

      Have you tested the water for ammonia, nitrite?

      Please come to the forum to post a thread under the fish section for further assistant. 🙂

    • Sure, if they are made for aquarium use. Regular plastic plants might leak harmful chemicals if they are not manufactured to be used in the water.

    • How big is the fish tank? What fish do you have? What filter? Any water conditioner?
      Please come to our forum and post a thread there with all the information. We will be better help you there. 🙂

  19. Hi my name is pj and i went to the store and i got 5 guppies and 1 angelfish and a bala shark and the angelfish had no problem with them no fighting or picking a fins. it a 30 gallon tank everything is fine! i woke up and feed them and 1 guppy was in a plant died i dont know what happen? they were fine swimming on top of the water and eating! please help

    • Hello PJ,
      Guppies might not be the best tank mate for the larger fish. There is also not enough information. Please come to our forum and post a thread there with what setup you have, and what exactly you did. 🙂

  20. About a month ago I got a Flame Angle, a cardinal, a Carpenter Wrasse, and a blue spotted puffer. In this past month all my fish looked fine, then on Saturday my Wrasse died, Sunday my flame angle died and on Monday my cardinal died. Each morning one died that fish has not eating and it was swimming funny when it did swim, then about an hour later it died. My puffer seems to be doing finer at the moment and I hope it will live.

    • Hello BlueAngel,
      How big is your fish tank? What kind of filter do you have? Need all the necessary information to figure out what might have gone wrong. Please come to the forum to post a thread there. 🙂

  21. hi there,

    I have a fishtank prob like 25/30L, we have 2 sucker fish and 4 tetras and 2 angel fish, we have lost two of our tertras Monday and Wednesday, but it seems the fish are starting to act weird, like not eating properly where they where super exited if its feeding time, they look a bit stressed do you think its the ph levels or what do you tink is our problem.

    regards
    Schultz

    • Hi schultz,
      You have overstocked your fish tank. 25/30L fish tank is not enough for even one angelfish. By the way, what kind of filter do you have?
      It is most likely there is ammonia and nitrite spike in your fish tank. Both substances are toxic to the fish. It is what happens when you have a undersized fish tank with too many fish, with no filter, and not cycled the fish tank before getting the fish. If you come to the forum, and post a thread under the fish section, we will be able to better help you. 🙂

  22. I used bottled aqua culture pre conditioned water in my tank , aquasafe conditioner , safestart in 30gal with a 20-40 top filter, and a bottom gravel filter. Why do my tetra fish keep dying and my placo lives? 100w heater keeps water at 78°-80° 2 air pumps uv light. Have 2 plants that are fine in there. What am i doing wrong? I don’t want to get anymore fish till the problem is fixed. I match the temp with bag float for 20mins or so, i don’t spill bag water into tank. I use the float method and add 0.5 cups of water to bag every 4mins then dump half out into bucket, and repeat this 10 times. I don’t want to injure anymore fish. PLEASE HELP ASAP even the beta died. Only thing living is plants and placo. I’m more stressed than the fish. 🙁

    • Pleco is a hardy fish. Other fish dying left and right could mean there is something wrong with the water. Have you tested the water for ammonia and nitrite? Please come to the forum and post a thread there for further assistance. 🙂

  23. Hlo sir I bring 3 gold fish and 2 black fish (gold fish type ) from the same aquarium of the seller but next day one gold and one. Black fish died why i have a filter also but tehen i saw gold fish who died the colour of the gold fish in their tale has been somwhere removed so plz tell me plz i want tthe fish to live

    • Hi Ajeet,
      What size of fish tank do you have? What kind of filter? The type of water conditioner?
      If there is damage to the fish, then it could be aggression.
      Come to the forum for further assistance. 🙂

  24. All fish are died when will u rply
    Plz rply i want to buy some more but plz answer me to protect the fish from dying 😔😭😥😪😢

    • Hello Ajeet,
      There is not enough information to provide you with help. Please come to our forum and make a thread under the fish section with all the information on what setup you have, and what exactly you did. We will be able to help once we have enough information. 🙂

  25. Hi i added a new fish to my tank today and added him like you say to and he looked fine then the timer went out and the lights go out i was layinv in bed worrying because my angle fish was schocked by my anenome and he looked a little hurt (I had to pull him out of the anenome because he was getting schocked) and i came back out turned the lights on and boom all my were dead but one and he looked hurtin. Yes i have a filter yes i have lots of live sand well grown live rock and obiously an anenome what did i do wrong did the angle fish release a toxin did the new fish have a diesase… pls help

    • Hello Alex,
      A lot of things could have gone wrong. We need more details to be able to help. Why don’t you come to the forum and post a thread there with more details on exactly what setup you have, and what exactly you did. 🙂

    • Hello caroline,
      There is not enough information to give you an educated guess.
      Please come to the forum and post a thread under fish section with more details on what exactly you did before the fish died. Along with all the information including the fish tank size, what water conditioner, what fish species, filter type, etc. We can help you better on the forum. 🙂

  26. Hi,
    I recently got a new tank and one of my beginner mistakes were adding new fish immediately after i bought it (with the shops water, wich was bad aswell) now , my fish all died (9 of them) in 2 weeks
    ph 7.1
    kh 3°d (the° needs a line under it)
    gh >16°d
    NO2 0
    NO3 25
    I do know that my ph is good but i’m a little worried about the rest.
    when some of my fish were still alive , my aquarium was developing this brown/yellow substance on the soil (white gravel). i got told these were biatoms that grew and it was fairly common to find in newly set up tanks. Then the other forum told me its part of the cycle? i got really confused.
    I hope you guys could help me out!
    Thanks in advance.

    • Hello Simon,
      You are missing the ammonia reading. It is toxic to the fish. PH is not much of a concern as long as it is stable and the fish were gradually introduced to the new water. They can adapt. The most important thing about the water is to keep ammonia and nitrite at 0ppm. If you come to the forum and post a thread under fish section, we are able to better help you. 🙂

  27. oh i forgot to add that it kinda like started with one fish just casually laying at the bottom , and when i dragged my hand across the glass it just started swimming normally for a good 10 minutes. so one fish died , a week later another 3 did and only got worse. so i later found out they had the white spot dissease. Well i cleaned my tank , gravel with hot water and a small amount of dish soap , fully cleaned my filter and the decor pieces. It has been running fishless for about 4 weeks now , still creating the supposed biatoms (on gravel , plants , glass) i tested the water a small week ago with the values above. Now i noticed small white organisms on my glass , filter , plants wich seems to be hopping arround in my tank. My question is now, are

    are the values good?
    what is the green substance that is creating?
    what are the tiny small organisms ?
    Is it safe for me to add new fish in it ?

    Thanks in advance,
    Simon

  28. I kept 12 fish for around 7 years some time back (without water treatment). All I had was a filter and air pump. It was my first tropical tank, so I was very pleased with the success. However, I now have another tank with other fish in which all but the larger ones died suddenly after a while living with me. Within minutes they would turn black and die. Anyone know why that might be?

    • Hi Bastian,
      It can be many reasons why your fish died. Need more detailed information on what exactly you did before the fish dying to give an educated guess. 🙂 Why not come to the forum and post a thread under the fish section with more details? So people there can help you out.

  29. I lost my fish because it got dead in few days
    But i dont know why it happened
    Well there are still four fish left
    And i need your help
    Please give me some idea to save them
    i will be very thankful to you

    • Hi, Taranjeet,
      You might want to use our forum and post some more details of your setup, and what exactly you did. We can’t even begin to guess if we are left with no information other than the number of fish still alive.

  30. I bought 5 mollies and 5 tetras yesterday and this morning they are all dead. Thecwater was tested yesterday and was fine. What do you think might have caused this?

    • Hi Kim,
      When fish die so quickly, they must be in some kind of shock from the change in water conditions. Fish can easily die from large and sudden changes in water temperature, PH, and hardness, etc. Have you acclimated them properly when you introduce them to their new home? It is recommended to add the tank water into the fish plastic bag little by little every 15 minutes or so until it is almost all tank water.

  31. Hi,
    I brought 4 big Gold fishes and some small gold fishes, also some angel fishes recently in small plastic tub. within 3-4 days 3 gold fishes died one by one. i was using to keep in the filter water, might be PH value 7 or less. what is the cause of sudden death of these fishes.i did not keep any filter in the aquarium.my question is can i keep the fishes in the normal water or filter water?how many times i need to give the food per day?filter is necessary for this small aqaurium?what are the things need to be consdiered to save rest of the fishes? please help me.

  32. I’ve tried several times to keep guppies. I’ve had my tank cycled (19 gal) and all of them have died 24 to 36 hours afterwards. Any idea why ? It would really help. Also they never want to eat the ignore the food completely.

    • Hello melan,
      Did you let the fish acclimate gradually to the new water when you introduce them to your fish tank? Fish die that quickly usually mean they were in shock from sudden changes in water conditions such as temperature, PH, hardness, etc.

  33. Hello,
    I’ve recently bought a 10 gallon tank had it a month now. I had 2 mollies when I started it, but one died after about 2 weeks. The other died today. After the first one died I bought 2 more mollies and a Plecostomas. The Plecostomas died the day after i got it. I went back the next day and got another plus w gourami. One of the gourami is acting really weird and I’m afraid its going to die as well. I didn’t know anything about fish until they started dying I realize I should have done a little bit of research befors I bought them, however I thought how hard could it be, my mistake. I’m hoping to keep the rest alive. I changed the water once, but I changed all of it at once not knowing that wad bad. Also not really sure when adding water shoyld I first take the fish out before I treat it with chemicals? I did the thefirst time because I emptied the tank but not sure if when I take out some of the water and add new.

    • Hi Andrea,
      It is most likely your fish died to shock when you introduce them to your aquarium. The new environment is different from what they came from. The sudden change in water temperature, PH,and hardness was too much for them to handle.

      There is also the problem of a uncycled fish tank. Please refer this to Aquarium Nitrogen Cycle.

      Change all of the water in a fish tank is what you must avoid. Do partial water change instead. Usually it should be 30~50% to avoid too much change for the fish.

      The only chemical you need for your fish tank when you already got the fish is water conditioner. It is for get rid of chlorine.

  34. I assembled new fish tank 2*10inch and put 2angel fish and one other after t3_4days I put some fish on that the next day I remove some water from tank and fill with fresh water by putting 10drop anti chlorine and 10drop anti ich bt I observed after dat day my new fish die one by one. they move slowly and die. Bt the fish which put early they are healthy. What I do.

    • Hi Priya,
      Sorry for the late reply. I have not checked the comment section for a while.

      Your post is confusing. What is exactly the size of your fish tank? 2*10inch? That is not right.

      You do not need to put any anti-ich medication in the fish tank. Meds have side effects. They are usually hard on the fish. The only thing you need is the water conditioner, and must be in the recommended dosage according to the instruction.

      There is also a lack of details. Aside the fish tank size, we need to know what filter and heater are you using. How you have introduced your fish to the aquarium. Acclimate the fish is a must, or they might die in shock to the sudden change of water conditions.

      If you are still around, please come to the forum to make a thread under the fish section. It is easier to sort things out there.

  35. Hey, everytime me and my gf buy cardinal tetras or other fishes they all die ian a matter of hours , my gf always cries about this.

    We have a filter running in the tank 24/7.

    After we bought the fish (10 cardinal tetras and 4 pink danio, we placed the bags over an hour then just pour them in the tank .

    Any suggestions for us to help us , so that next time if we buy our fishes wont die , it also is waste of money if fishes die in a matter of hours especially

    • Hi Mac Denzel,
      You must acclimate your fish before release them. Water temperature is not the only thing they need to get used to. Other things such as water PH, hardness, etc. are equally important. They can’t get used to everything by just sitting in the bag. You need to add the fish tank water into the bag little by little. For details, please read the article.

      If you have any more questions, please come to the forum to make a thread. It is easier to answer your question there.

  36. Set up a new tank nearly a week ago. Let the water cycle over night along with the filter and heater. Bought 6 lemon tetra and 6 neon tetra and 1 bottlenose catfish. They were all good. Two days later bought two fancy guppies. Each time we introduced fish to the tank they sat in their bags. We’ve had the guppies for two days and one died this morning. Pretty much took him out of the tank as soon as he died. Is there anything we can do to prevent the other fish from dying? We have a 50L tank with filter and heater. Also tested the water and the pH level yesterday was a little high.

    • hi Georgia,
      From your post, it seems you have not acclimated your fish properly. Water temperature is not the only thing the fish must get used to before being released into the fish tank. They must also get used to other things such as water PH, hardness. They can’t be acclimated by just sitting in the plastic bag. You need to add some of the fish tank water into the plastic bag little by little. For details, please check the article.

      You might also want to do a fishless cycling before getting any fish.

  37. I just bought a 20 gal long tank
    I have a 50 watt heater set to 78-84
    I have filter and light, I brought home 6 fancy guy pies 3 just died within 15 mins and now I’m scared the rest will to what’s wrong? I used Prime drops
    Stabilizing drops, Quick start drops, water conditioning drops

    • Hi Ferena,
      First, you do not need all the “drops”. The only thing you need is the water conditioner if you use tap water.
      Second, you must acclimate the fish when you introduce them to the aquarium. Your fish are most likely die to the shock. For details, please read the article.

      Third, while it is definitely not the reason this time since your fish died within 15 minutes, you must do a fishless cycling before getting all the fish.

      If you have any more questions, please come to our forum. It is much easier to discussing back and forth with you on the forum.

  38. I’ve set up my 40 gallon tank, ensured the water is warm and around 76 degrees with a water heater, all levels are safe, tested with a kit. I put the plastic bag in the water for about 30 minutes before putting the fishes into the water. I have a filter that was recommended by the store. The water has the 5ml of water treatment added initially which made the water safe per the test. I added the new fish to the tank around 9pm, we went to sleep at 3am, they were doing great, I turned off the aquarium lights and we went to sleep, we woke up around 10am and 6 of the 8 fishes were dead, no idea what happened. I had 1 neon tetra, 1 platy, 1 angel fish, 5 glow light tetra, 2 golden snails, 2 black snails and 1 tiger snail. The neon tetra and the 5 glow light tetra were all dead overnight. Everyone else is doing fine. What did we do wrong?

    • Hello Nick,

      Although you have given time to the fish to get used to the water temperature, you have not let them to acclimate to anything else in the water. You needed to add some of the tank water into the plastic bag every 15 minutes or so, while getting rid of a little of the water from the plastic bag each time. Until almost all water in the plastic bag is from the fish tank.

      Fish can get shock and even die from the sudden change in the water chemistry such as PH, hardness. You have to acclimate them when introduce them into a new fish tank.

      By the way, from the sound of it, you have not done any fishless cycling before you got the fish. It is highly recommended for starting an aquarium.

  39. Hi
    I brought a aqua one 22l tank last week this week I got on test everything good to go so today I got my fish I got a gupie few neon few shrimp few mix penguin etc 1 maybe shrimp dead 1 neon 1 of the mix its my first tank I followed all advice was given help please

    • Hi Will,
      We need more information to pin point the problem.
      If you please use the forum section, and provide all the details of your aquarium setup. Information such as what filter, heater, as well as other equipment and supplies you use for the fish tank. Then we might be able to find the problem.

      By the way, have you done a fishless cycling before you get all the fish? It is highly recommended to get the fish tank cycled to add any fish or shrimp at all. Or the ammonia will build up over time and the toxic will kill all live fish.

      For more information on fishless cycling, please check the article of Aquarium Nitrogen Cycle and Fishless Cycling.

  40. I recently bought a few fish (a baby shark, 2 catfish, and an angelfish), both of the catfish died at the same time. One of them was just laying on one of the decor upside down, while the other one got caught in the filter. Now my angelfish is constantly swimming up.They died after awhile, the tank had everything pre-set up, we let the fish stay in their bags and put them in the water so they can adapt to the temperature more easily. We feed them as required, the water was filtered, and since we just got them recenty we didn’t have to change the water.

    • Hi Ang,
      Without knowing more details of your setup and what exactly you did, it is hard to pinpoint the exact problem.

      If you can come to the forum and please post some more details on your exact setup, such as fish tank size, filter model, water conditioner you use, etc. it will be a lot easier for me to help you to find and prevent the exact problem next time. 🙂

  41. My all fishes died suddenly.it was living from the last 3 years without any problem.cant understand the reason.mine is cement tank it can accomodate 2000lr water.more than 50 fishes died within one day mrng.no one is remaining.highly disappointed. kindly tell the possibilities

    • Hi Seena,
      Sorry to hear your loss. If you can please come to the forum and post more details on your setup and what exactly you have done before it happened, we might be able to pinpoint the exactly problem for you.

  42. Hi admin, I’ve read your article, it may help me to know what will be the problem.. i have 6 small koi fish in 20 galloon aquarium. they all died.. 2 days ago i general cleaned it, change the water. 50% new water and 50% old, put 8 bottle cups of antichlorine and setting it up in 4hours before putting back the fishes. Have I done something wrong? Did i put too much antichlorine that might killed them? Im planning to buy new fishes, what can you recommend me to do so that the new fishes will not die in the same water? Should I general cleaned it again and put new water? Thank you so much!!!!

    • Hi, Lou,
      Are you sure you used the right amount of water conditioner? Check the bottle for instruction. 8 bottle caps sounds a lot for just 10 gallon of water (50% of your 20 gallon).

      By the way, did you say you put the fish back? Did you mean you have removed the fish during the maintenance? You should not remove the fish. They can get into shock from the sudden change in water conditions. You also need to let the new water to have similar temperature first before using it.

      For more details, please use our forum.

  43. We are beginners, for fish. We bought a 29 gallon tank over the weekend, had it set up for 2 days and had our water tested at our local pet smart, all was good. We added 2 platys yesturday morning that we had in another tank had them for a few days, and they are doing great in the 29 gallon. Last night, we bought 5 neon tetras from a different store, so far I’ve lost 2 and a 3rd one is barley hanging on.othe 2 seem to be doing good so far! Any suggestions at why this happened?

    • Hi Louise,
      You did not cycle your new aquarium. Ammonia builds up in new aquarium unless you have cycled it before adding the fish.

      There could also be a number of reasons why it happened. Including weak fish (some fish farm mass produce weak fish in antibotic filled water), or/and shock due to sudden change in environment (water temperature, PH, hardness, etc.).

      Some fish are naturally stronger than others even they are the same species from the same batch. So they do not die at the same time under the same conditions.

      If you have more questions, feel free to use our forum where it is easier to go back and forth with messages. 🙂

  44. Hello Admin I had bougt a fish aquarium of 40 ltrs. 1 week ago but in a one 5 fish were die.
    Here it’s a begining of winter, should i buy a heater or their’s a other reason of death.
    Please reply fast it would help me a lot.

    • Hi,
      If they are tropical fish, you must have a heater in there all the time unless you live in a tropical area.

      An aquarium filter is also a must for all aquariums. It must run 24/7. It also needs to be cycled before you add the fish. The article has some of the details and links to more articles about cycling.

  45. I just wanted to say that I appreciate the fact that you have taken the time to reply to comments posted in this article for two years now. That’s commitment. 🙂

  46. If fish are cold blooded then why the temperature of the aquarium has to b adjusted…the fish should change their body temperature according to the environment in which they live….

    • Hi Fari,
      Fish have no body temperature to “adjust” to begin with. Their body temperature comes from the temperature of the water around them. If the water is too cold, their body temperature will be too cold. Yes, they can adapt to the change to a certain degree… slowly. If the water temperature suddenly dropped by 10 degree, it is more than most fish species can handle.

      Think of if you just took a hot shower in cold weather. As soon as you step out of the shower, do you feel cold? Yes? Fortunately for you, your body temperature is regulated by yourself, and thus the impact of sudden change in environmental temperature does not affect you any more than on the surface.

      For the fish, any change to the environmental temperature will affect all of them including internal organs, immune system, etc.

  47. i recently got four goldfish. when i first got them, i temporarily put them in a pretty small container. i then purchased a small 2 gallon tank that was taller but not as wide as the container they were originally in. it came with a filter, water conditioner, and a light. i filled the tank according to the instructions and put the directed amount of conditioner. i also added gravel (that i washed) before i put the water in. i also read that u should put the bag inside the tank water before they are directly put in the tank. so i did that and replaced some of the bag water with the tank water every 15 minutes. then i opened the bag and let them swim in by themselves. they seemed fine the next day with the filter on and i was feeding them about twice a day (no more than they could finsih in 2 minutes), then the day after that they started turning brown and seemed to be struggling to swim away from the filter (so they were all huddled under the filter) and the water was pretty dirty. i assumed the filter was too strong for them and they couldn’t fight against it so i only kept it on a few hours a day and to clean it, i replaced about 20% of the water. then a couple days later, one of them was dead and the rest were still brown. so i took them out of the tank and put them back in the container (the container didn’t have a filter) and now they last three are back to their original color and seem to be perfectly fine. why did the tank basically kill one of them? thanks so much in advance, answering questions after two years is pretty amazing 🙂

    • Hi Kim,
      The tank you got is too small for 4 goldfish. It is only 2-gallon, and yes it is too small for most filters out there. When a tank is too small, the water conditions can be unstable when there is any small change.

      The filter must be turned on 24/7 or it defeats the purpose of having a filter. It does the aquarium nitrogen cycle, and to keep ammonia at 0ppm.
      Turning it off most of the time, and clean it too often or not careful enough will damage its bacteria colony which are needed for the nitrogen cycle.

      However, even without a sustained nitrogen cycle, the ammonia concentration is unlikely be high enough to kill your fish so quickly. There could be other reasons for it. Too strong of a current could be one of them.

      One very important note, even if your fish look fine for now in your little container, they will not last long in there. Ammonia will build up and kill them eventually without a minimal sized aquarium and a 24/7 running filter.

      Thank you for the compliment. If you are still unclear or having more questions, feel free to make a thread on the forum.

  48. When introducing new fish, I’ll first let the bag sit for ~20 minutes before cutting a bit into the bag to “mix” the water. yada yada anyway I was wondering if it’s okay to do it like that, or if you 100% recommend what you’ve said previously

    • Do not “cut” the bag. The water from pet shops might have parasites and diseases in it. We do not want it leaking into the fish tank.

  49. i have 2 baby dollies, i had a male and a female from walmart (they died within a month, of course) and meh babies are still alive, its only store bought fish that die in three weeks, right??

    • It is on average. Fish do not live more than a few weeks after being brought home. Store bought fish just have a worse record since a lot of them are diseased weak fish to begin with.

      Without the details, we do not know certain what caused the death of the two fish you bought. If you had nothing in your fish tank and did not cycle the fish tank, then it is likely they died to ammonia poisoning. The fry lived could be due to the fact the aquarium is finally cycled or near cycled when they were born.

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