Uh-oh!
The problem is, if it's safe for everything in your tank, it's not as strong. Ich only affects fish, so I think you should take them out and put them in a treatment tank alone.
You move them with the same water, sand and some ornaments you can easily replace and treat all of your fish with copper for about 2 weeks. When one fish dies, the number of spores in your water increases greatly and in my experience, they pick one fish at a time to attack. The other fish may have it internally, that's why I say you should treat all of them.
I used Sea cure copper treatment and Anti-Parasite food for internal treatment. Leave the old tank set-up and the new fish in your treatment tank for about a month just to be sure all the spores are gone and your fish are cured.
I know this costs more than treating the whole tank, but I lost almost two rounds of fish before I followed this advice and it saved the rest of my fish!
Good luck!
Fishy1 :happyfish