Fish Dying in Good water conditions

[Beagley]

I have a 55 gallon tank. The past year I have had 5 tiger barbs and a pleco. Recently I added 5 more tiger barbs, 2 pictus catfish, and a clown pleco. I also added live plants at the same time. The first week all the fish were doing GREAT. The second week started with both catfish dying, then my older tiger barbs, and each day one or two more have died. Now I only have my old pleco and a few tiger barbs. The temperature is perfect, water has been tested multiple time and tested good. I have no idea what is going on.

[Caliban07]

Originally Posted by Beagley

I have a 55 gallon tank. The past year I have had 5 tiger barbs and a pleco. Recently I added 5 more tiger barbs, 2 pictus catfish, and a clown pleco. I also added live plants at the same time. The first week all the fish were doing GREAT. The second week started with both catfish dying, then my older tiger barbs, and each day one or two more have died. Now I only have my old pleco and a few tiger barbs. The temperature is perfect, water has been tested multiple time and tested good. I have no idea what is going on.

Hi.

Fish produce ammonia which is toxic to aquatic animals. Big fish produce a lot of ammonia. Every aquarium over time will grow organisms that detoxify ammonia. If you load the tank with more ammonia than the organisms are capable of detoxifying it will build up in the water and kill your fish.

The process in which organisms reduce ammonia levels is called nitrification. Please research the nitrogen cycle. Hopefully someone can provide you with some useful links from the Aquarium Advice pages.

[Autumnsky]

Hi, the link is in my signature. Welcome. I am so sorry about the fishes deaths. It is also possible they could have had some sickness.

But did you change the filter pad around the time you got the new fish? Or change anything like the substrate, or remove a bunch of live plants?