I have a 90 gallon fish tank as my bait tank at home, I kept cichlids in it for years I'm very experienced with fish tank upkeep and maintenance. 950 gph pump, carbon to remove ammonia and other toxins, bio balls for biological filtration, I change water every two weeks 50% I've never had issues keeping fish of many varied species but I struggle to keep bullhead alive in this tank for more than a week or two. Around there fins a perfect circular ring is apparent on the skin of the fish and this happens before they die. Anyone know what might be killing off my bullhead? This is a reoccurring issue been happening all year! I've kept bluegill, crappie, warmouth, chubs, suckers all without issue. But the bullheads die in a week or two?.. I'm stumped?! Maybe something in my tank has a negative impact on skin fish compared to scaled fish? I will take some pics next time I stock up. I normally use most of them up but I live right on the river I fish and like keeping them for bank fishing so it would be nice if they lived longer.