google micro scrubbing bubbles reef and you will find plenty of articles on it. elegant corals started the method years ago. there is threads on here as well. tiny bubbles injected in the tank for several hours. I used a $10 air pump and a $5 wood air stone. helps pick up detritus from even the smallest of places so your skimmer can remove it. in addition it irritates some corals causing them to release mucus which in theory helps remove toxins from the corals. what I like about the scrubbing is it keeps the tank very clean.