As per title, I'm in need if some help deciding on an appropriate treatment for my daughters beloved "Nassa". He's about a year and a half old and around 6", 55g tank way over filtered with a corner mattenfilter setup, only tankmate is 4" albino bristle nose, 0 ammo 0 nitrite and less than 20 nitrate, temp 76-78f. The issue: he's just not been himself for a while, although still eating robustly. Right flank is slightly larger than left side, barely noticeable. He looses and gains color rapidly throughout the day. The main worry is a black splotch on right side that appeared over night two weeks ago and he's been rubbing on the sand substrate here and there. After a water change(20-30%) the spot will nearly disappear for a few hours, water changes are once per week usually but more frequent lately. He seems to swim normally but has been sitting on the bottom in a corner occasionally but perks up around feeding time. Been feeding peas for a couple days, effect has been minor. Normal food is hikari cichlid gold and hikari sinking wafers, earth worms or frozen foods occasionally. Sorry for wall of text and any help would be greatly appreciated.
