There is a medicine that is ok to use on coral and live rock. One is ick attack the other is microbe lift. They have both worked for me and they're safe for corals and rock. A UV
sterilizer is a good investment and so is a 10 gallon hospital tank. It's kind of frustrating because ick is treatable. I had the same problem and learned from it. If you get a hospital tank you can treat the fish with copper and problem solved. You don't need a skimmer or t5 lights for the hospital tank. Just the tank, some PVC
prices a heater and a cheap light. No sand needed.