The tank is a 100 litre tank. We have an asap 700 filter in the tank. The uv
light is turned off every evening and all through the night. We have no heater in the tank as we are aware that they like the cold water. They are just common good fish all three the same. The one that swims around is the largest but we have had them about 8 months now and they have all been fine together it is only these last few days that two have started to hide. The one that doesnít hide is the only one that seems to have what I can only describe as bruising on his skin/ scales.i am aware of the cycle and what this is, we have an ammonia reader in the tank that tells us the constant ammonia levels and we also have one for ph in the tank. We do regular water changes 20% each week and when we noticed they were stressed like this we did an immediate 50% water change. We feed the fish pellet food from pets at home. That swimming fish is the largest as seen in the picture the other two are smaller than that one.