*nods* Yes, yes. Stable numbers. And feeding an addiction to fish. XD
Tiki, Sluggles could have fin melt/saprolegnia. Sapro is practically the only true fungus that occurs with bettas. Others only look like fungus but are bacterial. Try Betta Revive on him. It has malachite green which works on sapro. For Derpy, stringy poo even if it isn't white probably means parasites. Try General Cure.
You can get actual malachite green but treat Sluggles in a tank or container you don't care about if you do. The stuff stains and won't ever come off.