The little I know about them is that they thrive in high nutrient conditions. To control them, I would say just keep up with water changes and don't overfeed your tank. To eradicate them I really don't know or I would have gotten rid of mine. I believe I was told recently though that using a kalkwasser mix as you would with aiptasia will work on these as well. Hopefully James will stop by and post an oppinion as I believe he was the one I was discussing it with. (Cindy passes the ball...)