My dad currently has a 47 gallon bow front tank. He came home yesterday morning and found all 4 of his clown Loaches floating at the top. From what he told me, they all had like a white/clearish coat on them that was almost peeling off. They've all been eating fine and active before this happened. He checked his water with a new test kit and he said it is good. Any idea what it could that killed them that quickly overnight, and would the other fish be in danger?