With the yellow zoas, my recommendation is to find the spot in your tank they do the absolute best... and then drop 1.5 inches. That way they will still grow, but at a slightly slower rate. You can feed these guys, they are voracious eaters much like those bloody aptasia are. Fun to watch.
Just dont have their rock touching anything you really care about. Or next thing you know, you'll have it on your kitchen counter, with a hypodermic needle, nuking them one by one and scrubbing off the remains. They give a great pop of color in a tank, but damnnnnnn!