Sudden ich outbreak

Hello. I have had my 75gl set up for about 8-9month. Everything was going well until this month. I added a blue hippo to top off my fish with the plan of adding corals after a few months. Suddenly the hippo got ich, just as suddenly it went away. This continued for about a week until it got it really bad and died. Now all the rest have it (fox face, coral beauty, flame angel, kole tang, and marine betta) only my o.clown pair seems to be un affected.



I don't have water parameters I usually take my water to a lfs and it always comes back perfect.



I have no idea what to do or what caused it. Any help is greatly appreciated.