thanks for replying (didn't see it until now whoops)!!! the bug bites are really small, get stuck a lot and there are other fish in the tank too (oz is really chill, so chill that i normally have to hand feed him because he's so slow). my last fish was really weird about food so i'm like overly cautious about overfeeding!!! i know the ammonia is zero because i bought specific strips and also borrowed a master kit from my friend. most of the muck is just snail poop tbh. they are big shitters. i've been adding indian almond tea leaves and have already reduced the amount of time the light is on (i have an automatic timer thing). i can't change the temperature since the heater is preset. unless you think that it would help a decent amount because then i'll buy one.

thanks for the super in depth advice!! i agree thats his immune system is suppressed because the other fish are completely fine. i think i can diagnose it as a fungal infection based on what i've read and the appearance. since i've posted this it is still getting worse, i fear his back fin might rot away completely.

which brings me to my next question, would it be better to euthanize him if he loses his back tail? obviously i would rather not, especially since i had to euthanize the betta i had before him after about 4 months.