There are many ways to treat ich, I tried a method but didn't have any luck cause I killed my two fish by using a quaranteen tank and doing a hyposalinity treatment. I think my downfall was that I didn't have an accurate way to measure my salinity (I had a hydrometer, which I found out afterwards was WAAAYYY off ). Your best bet is to research Ich and go from there.
It is a parasite that has a strange life cycle inwhich it attaches to a fish, eats a little from the host, drops off in to the water. At this time it seems like the fish is all better, but then the parasite reproduces in the sand and comes back again, just 10X stronger. There are copper medications, but that will kill your snails, corals, ect. so you would have to do that in a quaranteen tank. I have heard that garlic will help, but I don't know if I would want to soley use that. A UV could also help, but yes it is expensive. Do some reading on UV to see if its worth it. If you take all of the fish out of your display, and treat them for ich in a qt tank for about a month you can break the life cycle of the ich parasite in your display tank and at the same time cure the fish of the problem that is on their flesh. This takes time and good test kits to make sure your parameters in your qt tank are stable (could have also been my problem).
Do some reading online about ich, its life cycle (I believe its important to understand what your fighting here) and all potential treatments. If you have any questions please feel free to post here or PM me.
Good luck!