I like the Mardel brand. Maracyn-Plus is usually a safe bet. I have to warn you, it can be hard to dose in a small tank, so try to get something that has a dosing like "one drop per gallon" rather than something you need to cut up a pill for. Some of the gelcap meds are powder inside a caplet, which makes it really hard to dose. The AP Anti-Fungus med is easy to dose in small tanks, and should take care of the problem.