Best thing I have used short of pulling the rock out. Pepper shrimps are hit or miss. They do eat the stuff, but from what people say they are picky about water flow...ect.. Mine did not do anything. nudibranchs eat them. Kind of expensive tho. As you found out, they grow fast. If you bother them, then they will put more seeds into the water and more will grow. aiptasia-x is easy and kills them within seconds. By easy I mean that you only need to squirt the stuff right on top of the aiptasia. (they think it is food and stay open) Free things that work - Hot water, Lemon juice - only problem, like some of the other paid solutions is that you must inject the stuff into the stalk. Easy if it is big and on a rock. VERY hard if it can suck itself back into a hole/crack. If you do go with a chemical then just read the box on how it must be used. (ie: inject into stalk or just squirt on top)