Fungus Guard by Jungle - Sodium chloride (aquarium salt), potassium chloride (good anti-fungal), triethylene glycol (slighty weaker, broad range antifungal/bacterial), EDTA (aids slime coat), methylene blue (pretty good anti fungal), polyvinylpyrrolidone (aids slime coat), nitromersol (?), and acriflavine (?).
*acriflavine will kill plants and beneficial bacteria.
Jungle Fungus Eliminator - sodium chloride (aquarium salt), nitrofurazone (fungicide/bactericide), furazolidone (fungicide), potassium dichromate (fungicide).
Hope that somewhat helps you. Fungus Guard seems more powerful to me, of course it all depends on things such as concentration, not just ingredients.
Is this persistant? Just reread the question. I'd get something directed more at bacteria. Have you tried aquarium salt?