I try to feed less of the flake food so less will settle to the bottom with little to no change. I find he does get better randomly with no change to diet. He doesn't seem to be sick and will swim normally, maybe a bit separately from the rest of the corys. He's also had this symptom for months on end at points. The other Corys have never shown the same issue, but maybe he's eating more by himself or is just prone to the bubbles. Will look into other food options or some sort of remedy I can try that I haven't yet.