One day I noticed that one of my older cherry barbs was swimming upward, like he was struggling to stay afloat. I thought it was swim bladder disorder, and I did everything I could, but he died, I think from exhaustion. Then two of my younger barbs stared swimming like they were struggling up against a current too. I tired all sorts of medicine and parasite removers, but they still haven't recovered. I herd swim bladder disorder makes them struggle to stay down, not up, so what is this? Nitrate levels in my aquarium where high, but I got them down with some big water changes. I have 30 cherry barbs in a 20 gallon aquarium w/ plants (I know that's too many fish in one tank, I used to only have 3 cherry barbs, but they had a bunch of babies.)