I lost all my fish in my 210 display tank because of ich.
I put in a uv
sterilizer and let tank run with just my corals and inverts for 8 weeks. I also cleaned my sand bed with regular water changes. I did not use any chemicals or treatments. No problems since.
I also use a QT now with canister filter. No sand because that is where the ich likes to hide when it is not killing your fish. When I am not using my QT I clean the canister filter with RODI
water and let it soak in it for 24hrs. Then I hook it up and let it run off my sump on my display tank building up the bacteria in the bio media until needed again.