I took one or 2 at a time out put them in the water from my tank & quickly scrubbed them, I did sit the rock on a towel till I finished cleaning all the rocks then put them back in, I would say they may have been out 20 minutes. I did find the mantis that was killing my snails. You think that was too long to be out of the tank? I didn't take out the rock the anemone was on. My anemone looks good again...weird. I am going to check my water again tomorrow & do another water change if I need to.