Ive had my tank up and runninf for about two months. Its a 46 gallon bow front tank. I have 18 platys 3 swordtails 4 angelfish 4 cory cats 1 pleco and 4 snails in it. 4 of my platys now have this white stuff on their fins. I dont believe it to be ick. Can anyone tell me what it is?