Agressive johanni causing ich

My johanni has been picking on my female peacock and stressed her out enough to catch ich. However i just noticed that he has caught it as well. He is causing major upset in my tank. Before i got him my tank was peacefull but now everyone is irritated by him. Any ideas on how to reduce aggression quick. I dont want the ich to spread to my other fish. Also i was thinking of starting a treatment but last time i used it, i lost more fish to the medicine. The malachite green was too much for some of them i guess. Before this medicine i used kordans ich attack, which wasnt as strong since its organic. So any reccomendations for ich treatmeant