I have a 6 year old Shubunkin in 75 gallon tank with 2 friends that has been very healthy until recently. A few weeks ago he has some buoyancy issues and would be listing to his left badly, he was treated with erythromycin, first just a recommended dose with soaking for a week, and when that didn't clear it up and did a regiment of recommended dosage every 36 hours for a week into the tank and that seemed to mostly clear it up, possibly a slight permeant minor left lilt but swims and eats normally.
However he's been sitting on the bottom a lot more this week. I've also noticed in the last few weeks that he has these black areas at the base of his front left fin, and two on underside that are likely more recent, a few smaller black spots I think are really recent. There is also some minor irritation in that area from sitting on the bottom. This morning I can tell he is stressed, breathing slightly elevated but still excited to see me, I think his front half is slightly swollen and he now also has a 'bubble' coming out from the side of his gill plate and I'm extra worried. (see photos for bubble, black area, body condition)
I dosed the med trio this morning (erythromycin, prazipro, ichx) and salt level 1 (1 tbsp per gallon) per the blog.
Does anyone have any thoughts as to what could be ailing him or treatment advice? I'm thinking internal bacterial infection but possibly something else as well, is there a type of black external fungus/mold I can treat for? His tankmates seem fine.
co-op test strips confirm my normal tank readings, nitrate between 25-50, nitrate 0, hardness of a rock 'cause texas water, kh 120-180, ph 7.6, 0 chlorine, ammonia reading as 0.5 (aka chloramine normal reading for my tank and tap). Tank gets 50-60% conditioned water change every 2 weeks.