Lately I have had the worst luck with my bettas.
This is the second one to have torn fins. Strangely, it's only his back fins and none of the others. But I'm trying to determine the cause, and I'm at a complete loss. I have been putting fungus guard in, just in case, along with some stress coat. but I'm not actually sure if its fungus or mechanical. I've checked the tank over pretty thoroughly for sharp things that could tear his fins, but haven't found anything. It'd be a pretty odd place to tear if that were the case, anyhow. I've also heard of bettas nibbling at their own fins. I suppose this is possible, but I've never caught him doing it. I've also noticed he hasn't, er, been regular as when I clean the tank I don't find any leavings.
So I was thinking...maybe it's something I'm putting in the tank? All ammonia, NitrAte/rite levels, and ph are fine, but maybe it's some of the water conditioners I've been using? Currently he's in a 2.5 gallon with a small heater that keeps it at 80-82 degrees. He has a small filter that works wonderfully.
This is what I use for water conditioner:
Jungle Ph Decreaser (liquid form)
Prime (takes care of NitrAte, chlorine, and ammonium...although, I should note that i have to use much more than the directions say to because there is a lot of ammonium in the tap water here...possibly from farm runoff)
a tiny bit of aquarium salt
almond leaf conditioner for bettas (liquid form)