Hello coralbandit -- Another member recommended I contact you to ask about using Melafix in a Betta tank. Roughly 12-gallon (actual water capacity) tank 48'Lx6'Wx12"H divided into thirds with three male bettas; gravel substrate, live plants, two larger river stones in each section and sponge bubbler filters in each. 50% water changes weekly until the last 3 weeks. In that time my tank has been clouding up rapidly; I've been doing 75% - 90% water changes about every 4 days. I keep the temperature within one tenth of a degree during changes; use Stress Coat with each change. The last water change was Sunday and the chemistry was well within acceptable parameters. It now appears that the fishes are rapidly developing fin rot. I began using Melafix yesterday, but have read conflicting articles concerning its use with Bettas. I was told that you are the one to ask.