Maybe you could try an experiment. In a bucket or 3 lb margarine bowl (or similar), put 25% H202 and 75% rodi and a brushed off rock in it over night. Then brush it off again and put it back in until afternoon. Rinse well with rodi and put it back in the tank. Watch to see what happens. It should die off. Cuc should also try cleaning it the rest of the way. If it works, you can do 1- 5g bucket of rock every few days. This is what killed mine off along with using good snails after the soak. It never returned. The bios of the rock will return once back in the tank. You might also do a wc or 2 during the process if you do the whole tank. But you can't put corals in for more than a couple minutes.