I put all my fish in the (H) tank to do hypo for ICH and this has come up on this fish. He has had it before but not as bad and it went away. He first got it the first time I did hypo on him so I think that low salt brings it out. The bad thing is that my other fish show signs of it. Some of them have stopped eating but not all of them. Most of them are very active, him included. I have had all these fish for over 3 years, good health. Why is it and what is it?