Sick cats

I bought 4 hoplo catfish from chain store couple days ago..yesterday I posted in another section, but symptoms have changed. I now have one cat with serious fin rot, and two that have pretty serious ich. Fairly sure I might lose the guy with rot, but the two with ick dots are behaving fairly good otherwise. I have Coppersafe that has worked for bettas in the past, but worried about dosage. Would they be okay with say, 3/4 dose? Or would that aggravate disease to be non respondant? What about the fin rot guy? I have melafix?

Well, my fin-rot guy did die. Right before I got your message I had put about 1/2 strength coppersafe in tank,..had to do something, was going to work for 12 hours. Raised temp up to what I thought was 85, but I think its more like 83. Need to put another heater in if I raise temp. I think I probably should. But they have slowly improved to the point where there is only a few spots. Still, I think it should be gone..its almost time for disease to go "new generation" and I'm worried. I have metro crystal, Quichcure, and more coppersafe. I understand your distrust of the copper..it is a heavy metal, but so is salt a "heavy mineral". I'm not sure I trust salt any better, though easier to overdose with copper. Happy they made it so far, but I have to move to stop this and not sure what direction to go. Thinking, raise temp, add more coppersafe. Not sure.