if you can take the rock out, chisel them off. wear gloves and a mask and eye protection. I did it during a water change using the dirty water and two sets of clean water. I chiseled them off under the dirty water, rinsed the rock in clean water and used the 3rd for the water change. I only did a little at a time. For the larger infestation, I took the rock out and bleached/cooked rock in the sun multiple times for 6 months.