This morning while feeding my juvenile Yellow Perch I noticed that the lone YOY Bluegill in the tank with them (that's only half the size of the perch) was really beating on all of them and biting at them quite aggressively. Because of this, I moved the 'gill to its own 10 gallon to let the perch recover. Upon inspecting the perch now though, I just noticed that they all have several white spots spread all over their bodies. I'd been wondering why they've been acting weird for the last week or two and now I think I have my answer. I originally took home 16 perch to split between me and a friend after I quarantined them but in the past week and a half I'm down to 12 perch. The ones that died all did so overnight and symptoms the day before included freezing in the water column nearly straight up for several minutes at a time. My theory is that the Bluegill bullying the perch lowered their immune systems which then led to ich taking over. So now I have a dozen sick perch I need to treat for ich, one of which is already close to death and showing the same levitating behavior as the ones that died did. All of the perch share these characteristics now though, they're covered in white spots, the area that I believe would be right behind their stomach looks sunken in, and the ones that are about to die float vertically and motionless in the water column. They're all together in a 10 gallon with a sponge for filtration and get fed twice a day (either frozen bloodworms, mysis shrimp, or daphnia), water changes are every 2-4 days and are 50% with new water being around 68-72° (the coldest I can get in the summer). They're all still feeding well and acting fine (except the one) but I can clearly see the white spots on their bodies. The Bluegill as of now seems fine with only the tinyest white spot on the bottom of his caudal fin that is probably just a nip mark if it's anything at all. So how should I go about treating the perch? I'm afraid to take the heat approach since perch are cool water fish and their water already sits at 74-76° in the summer. I also don't know how much salt this species can tolerate so right now I have half a tablespoon of salt in their entire 10 gallon tank. Any advice or help you guys can give me would be greatly appreciated as these are awesome fish with great personality that I'd hate to lose.
Thanks for the help!