One of my female bettas in my 10g sorrorrety tank just died today. She was fine yesterday, not a mark on her at all. Today she was dead. She had a white cottony growth on her dead body. I was looking at the tank a minute ago and found more of the cottony stuff on the substrate. My question is, what medication should I use to clear it up? I have never had much luck treating it with aquarium salt in the past.