I know this isn't for my fish, but my brother has a veil tail betta fish in a 5 gallon tank. Good filtration, all betta-friendly stuff for Stuart. Recently, Stuart got some kind of scale thing one one side of his body. My brother got some sort of leaf-nature package (can't remember what it's called) and turned Stuart's tank into a dark tank. Fast forward to today, I get home and my mom told me that Stuart had lost his ventral fin and his tail was looking ragged. My brother finally did the first partial water change in a good while, and they used some of the treatment stuff I've got and they said Stuart perked up a bit, but are still a bit worried he won't make it through the night. Any idea what Stuart has?