Hello. I'm needing some advice on my recent fish deaths. I have a 75g freshwater tank, which I started in July of 2016. I have mainly tetras and angels, but I also have a couple of gourami, plecos, small catfish, and 4 giant danios. A couple of months ago, many of my fish began mysteriously sitting on the bottom of the tank an dying within 24-48 hours. I have a large Marineland backpack filter (suitable for up to 80 gallons). After reading about proper filtration practices, I have since added a second backpack filter (also suitable for up to 80g). This added filtration really seemed to help. However, 2 weeks ago, I purchased 3 black angels and 2 pearl gouramis. All 3 angels have died (the first 2 within the first 3 days and the last just today). The gouramis seem to be doing fine, but today I also lost a dwarf gourami, which I have had for over a month. I just completed a water change. Before the water change, my nitrite and nitrate readings were normal. I usually change out the water every 2 weeks. Could I still have a filtration problem? I read an article on here about the power of cansiter filters. One other note, the large black angel that died today seemed to have some frayed fins, yet I never witnessed any other fish picking on it. The other deceased angels' fins looked normal. Thanks in advance.
In my experience, fish will not die quickly (within 24~48 hours) if it is a filtration problem. They usually last for days to weeks or even longer.
Your situation sounds more like the fish were in shock. Did it happen right after a water change?
I personally had made the mistake of letting the fish get into shock after a large water change. The problem was the temperature of the new water. It was about 6F below the tank water. That was enough to get the tropical fish in shock. Basically, any kind of sudden change in the water can get them into shock. Things like water temperature is just one of them. Other things you need to pay attention to is the water PH, hardness, and even nitrate concentration. Sudden large change in water perimeters will kill the fish very quickly. You can see the sign right away after the water change.
After my own incident which killed off more than half of my fish (many years ago), I started to use an extra aquarium heater to make sure the new water in the water bucket has similar temperature to the tank water.
Another thing is, how much water did you change in term of %? Usually 30~50% partial water change every week is recommended. Too little won't remove much nitrate and other organic waste. Too large of a water change will contribute to the possible "shock" effect due to the buildup of nitrate and the change of PH as well as water hardness. Water change every two weeks will also have more nitrate buildup along with PH and water hardness change. Basically, I recommend 30~50% partial water change once a week over your current routine. It will not only optimize your water quality, but it will also minimize the difference between the new water and the tank water.
If there is a problem with the filtration, you should check your water again for ammonia, nitrite readings. These two readings must be 0ppm or there is a serious problem. Nitrate is ok at even 40ppm+ for most fish, since it is not toxic like the other two chemicals.
You do not need a canister filter if your ammonia and nitrite readings are at 0ppm all the time.
I also recommend minimize the feeding. Too much food will pollute the water to cause ammonia and nitrite spike.
Thanks for your prompt response. In fact, I did do a 25-30% water change as I was introducing the new fish. I bought some more live plants and decided it would be easier to plant them with the water level down. After returning home yesterday (from being out of town all weekend), I noticed 2 more of the new fish had also died. In total, I had purchased 9 fish. Is this simply too many at once? Did I overload my system?
As long as the ammonia and nitrite readings are at 0ppm, it is not "overloaded". You need to double check on these readings to make sure. You have a filtration problem only (if) there is indeed ammonia and nitrite, even trace of it. Otherwise there is no need to look that way for better filtration system since it is not the problem. It is a good idea to use a liquid test kit. It is more accurate.
I still think the problem could be the shocking effects from the water change. Either that, or the fish are actually of low quality. Some fish are bred from low quality fish farms with weaker immune system. They are more likely to die even when the healthy fish are doing perfectly fine in the same fish tank.
By the way, double check the water temperature to make sure it is ideal and stable. It is also one of the first things I check if there is a problem. Followed by testing the water for ammonia and nitrite. We have to rule out the possible problem one by one.
