It's only dangerous if you let it squirt in your face or somehow turn it to gas form and inhale it. The best way would be to remove the rock and use a wet saw to cut them off. I don't have a usable eye saw so i use a pair of bone cutters and cut them off with small chunks of rock. Then you can glue them up frag plugs and sell our give them away. Bone cutter cost about $10. If you try to peel them off the rock you'll most like kill them.
Depending on tank size, may want to run some fresh activated carbon you remove any toxins in the water. I usually change mine as a safety precaution when i do a lot of fragging.