if you want them to grow, glue them or wedge them onto a dead coral skeleton. preferably the calcified skeleton of another calcium consuming coral like an open brain. some plugs are made of that same material and they will grow fast on those also. they do not grow very fast on rocks. that and spot feed them and dose calcium. find the good location in the tank and do those 3 things and your acans will produce like 6 babies in a month or 2