Hello, I built a new tank for my juvenile swordtails. I upgrade the tank from 15 gallon to 40 gallon. I move 2 sponge filter, cycled, from the last tank. It's started about a week ago. There are 25 juveniles there and I put 6 corydoras in the tank and 2 adult molly. The problem is, some fish started to die. Yesterday I lost 3 of the juvenile. In total I have lost about 10 of them and 4 corydoras. I have do water changes every 2 days. But after I do water change, i'm still losing my fish. Any problem have I done to my tank? There are some moss in the tank, but I just added when I started the tank, so it's just not too much. Can anyone help me with the problem? And any solution?