I have a betta that I have experienced similar problems with. I haven't actually ever seen parts of his tail but just noticed each evening that more was missing. All I had in the tank was a whisper 10 filter which has no sharp edges either. I tried melafix for almost 2 weeks, added a heater and an air stone but nothing helped. I finally decided that it wasn't fin rot and moved him into a breeder box inside my 29 gallon. His tail is now healing without medication. He always liked to swim down under the filter and then back up behind it. I guess he was tearing his tail and fin on it some how. I want to put him back in his tank but can't figure out what to do to make it safe.
I just got done cleaning my tank around 15 minutes ago and noticed there is a piece of tail hanging off of my babys "butt fin" .. and then I also noticed that several strands from his fins on the bottom of his body were floating in his tank and the thing that stumps me the most is that he lives there alone and there is nothing in that tank thats sharp or nothing that could rip them off.. so .. HEEEEEELP!!!!!!! ...
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