I have 30 lbs of it in my fuge. My only beef with it is that unless I use filter socks, the particulate matter in the water column gets pretty high. I can't seem to get culerpa to grow in the fuge; my nitrates have always been undetectable, so that may have something to do with it. I don't know what it is made of, nor do I care. I have zero algae in my display and run totally skimmerless; everything is doing great.