So my betta used to be in a 40 gallon community tank with a bunch of platies. He started losing his fins after about 2 months in there, and I assumed it was platies since it seemed like perfect half circle bites had been taken out of the fins. Unfortunately I didn’t have money to set up another tank at the time, so he ended up losing his dorsal fin. During that time he did get fin rot with the classic cottony growths, so I treated that with Maracyn packets as directed and it seemed to stop (the fin rot at least). Then he started having bites taken out of his tail fin (it didn’t seem like fin rot anymore cause whole sections would disappear overnight), but I finally had the money for another tank and set him up on his own in a 9 gal Fluval Flex.
He seemed to be doing better for about a week, but now it’s progressing even worse. His tail fin is almost halfway gone, and his bottom fins are starting to go too. I don’t think there’s anything sharp enough for him to tear them on in there. He does sleep right on the sand and it is a courser grain (imagitarium black sand from Petco) but in my opinion it doesn’t seem rough enough to be causing the damage (also his tail fin doesn’t touch the sand, in his bottom fins.) Also today he tried to jump and smacked his head on the lid, which he has never done before (I work from home for 10 hours a day and both my tanks are in my office so I have a pretty good idea of normal behavior). I’m pretty sure he doesn’t bite his own tail either because he’s a dumbo plakat so his tail isn’t super long and flowy. I’ve posted water parameters and photos below. I’m not sure what to do at this point.
Side note: he is much less active in this tank, I think cause it’s smaller and he’s alone. I’m getting 5 Pygmy Cory’s as soon as I can, but he does eat normally and interact with me when I come up to it.
Water:
pH 7.6
Nitrates 5ppm
Hardness ~250 on an Aquarium Coop test strip
Nitrite 0
Ammonia 0
KH/Buffer 161 ppm (API master kit reading)
Water Temperature 79-79.5
Also here’s what he looked like about 1 week after I had him.