Keeping fish in an aquarium can be fun, and it is one of the most popular hobbies among pet keepers around the world. Sadly, the truth is that average fish only live for 3 weeks after sold on the market.

My fish is sick! My fish is dying! My fish just died! Why? What caused the fish to die in such a short period of time?

In at least over 95% cases, fish die early because of the following common beginners’ mistakes:
1. Tap water was not treated with 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 filter at all)

For reason #1,
You must know that fish can’t survive in untreated tap water. Tap water contains chlorine and chloramines. While Chlorine is said to be 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 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,
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 result in the fish’s death.

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 there is too much water for the container to handle. 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 removed/added 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 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.

The above scenario is based 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 needed 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,
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 would recommend AquaClear power filter for small sized 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 pleased 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 that ammonia gets removed 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? No fish should be added 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.

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