Thanks. I have a little knife fish (5") and he is very sensitive to something. I am guessing fungus from my reading/research. I thought it was maybe onset of ich, but heat & salt as prescribed in this forum have no effect. I have perfect params, do weekly changes, etc. He is very active and has a ferocious appetite. Looks like his scales are shedding in small sporadic spots. I also read that fungus can be living in the substrate and hoped to find another answer besides drain the tank, remove all of it, and rinse with bleach.