Your display tank needs to remain fishless for 12 weeks to rid the tank of ich. You need to put your fish in a QT tank and treat him by using one of three options. Copper, tank transfer method, or hyposalinity(IMO hard to pull off). I am not certain but I believe firefish have a hard time surviving ich. Dipping rock or anything else in freshwater or any reef safe treatments do nothing. In the future if you Qt your fish you will not get ich in your DT. There are many stickies in the new to hobby section and fish disease section. Failure to follow the stickies will most likely result in another ich outbreak at a later time and make your reefing miserable. just my 2 cents.