One of my betta fish is slowly but surely losing his fins. The mystery of this is that the cage is a "split" tank and the other betta fish seems very healthy: no fin splitting or disappearing.
I've tried changing the water, etc. Not working. At present the Ph is 7, the temperature is 80, they've had some antibiotic drops put in, as well as stress coat for a week and a half. The ammonia is "light green" but it's probably at zero, as no matter how much Ammonia detox I add, it never gets lighter than this. (False reading, etc.)
They live in a 10 gallon split tank. Changed 100% once a week.
No matter what I do, it keeps getting worse. I feel so sorry for the little guy.
Could this be stress nipping, perhaps? I'm not sure what else to do and what I'm doing wrong with this guy. Otherwise, he looks fine, but his fins are just in tatters.