That is a lot of aips. Are they only on that rock or are they that populated through out your tank? They also sting fish.
What size is your tank? When you start to kill them, you are going to have to do it in small amounts b/c all of them dying at once can cause an ammonia spike. The larger your tank the more of them you can kill off, the smaller the tank the less. With that many of them it might be easier to take the rock out and let it dry out in the sun for a week. Then place the rock in a bucket w/air stone (w/tank water) and let it run for a good couple of weeks. Then you can place it back in the tank when you are sure that all the decay is gone.
With that many of them, I'd also check any sump area you have b/c you may just find them there also.