I'm with ReefWars on this one. There are several types of "Clove Polyps" but I'm afraid the ones the OP is talking about are the small blueish/purple ones that can take over and entire tank in just a few months. In some tanks they stay confined in a small area for months and then seemingly overnight appear everywhere in the tank. One of the most beautiful tanks I've had the pleasure if seeing first hand was taken down and NUKED because of the "Japanese Clove Polyps".
I brought a few "Clean" frags home from this tank and I've been battling it every since with a LASER! It takes hours upon hours and I'm just "keeping up". They reproduce in several ways one of which is casting a "rice like" seed into the water column that will grow just about any where it lands. This includes powerheads, overflows and output from return lines. NUKE EM!!