You need a 72 day rest without fish (these were the only fish, right?) No fish in the display tank for 72 days, and since someone sold you fish carrying ich, DO please quarantine the next fish for 4 weeks in case you get another pair with the same. Use your 72 days to build up your inverts, even a couple of soft corals are ok, just no fish, no use of nets or other equipment between the 'safe qt' tank and the contaminated display tank. With water, comes the ich or whatever else can come across.
You DID NOT let water from the fish store into the display, right? Do a 'dry' transfer, ie, in a colander or small container with NO fish store water. Use your bare hand (and put the stopper in the sink!!!!) to get the fish from the bag into a gentle container with (if you like] qt tank water. Afteryour fish is in qt, observe him'/them very carefully daily.
What is a qt tank? A small bare glass tank which you should keep immaculately clean and change the filter floss daily (pillow floss from a sewing store is excellent for this. And cheap.
A dose of Prazipro is ok for starters in the qt tank. Give it its time, then put a carbon bag in the filter and let it run 3 days to take out the PRazipro. Beyond that, do not treat until or unless you spot a problem, and then consult here to get some advice as to what to use.
The ich parasite will starve to death without a fish to prey on. And it can't reproduce: a fish's fluids are essential to that process and you are not letting it have that.
Good luck. Your rock was not the cause of this. Your fish came from a tank that had a problem you couldn't see and possibly the store owner didn't see either. Precautions have to be taken by the buyer, like the isolation. And if you meet the same again, read up in the 'stuck' threads atop this forum (or over in the Fish Disease forum) on a process called TTM or 'tank transfer method.' Bear in mind you can use a polystyrene bucket as part of this process, so you don't have to buy endless alternate tanks.
Good luckl