I used them pretty much since they first came to market. They do work, in that they keep nitrates at zero and phosphates low but not quite zero. If you have too many, then you will need to dose other stuff like aminos etc. I don't know what else they strip from the water, but they do strip something. I got tired of the balancing act of fighting cyano, and trying to dose to keep my sps from bleaching out, and finally put a fuge online so the chaeto could grow while the pellets melted away. Best thing I ever did. Colors on my sps started to get deeper right away. The more the pellets melt away, the better my corals are looking. I look forward to having them melt away completely so I can go back to natural filtration. In my experience they are just a balancing act. They work but in proper doses and not as a sole source of filtration. In my opinion, a small amount in adition to whatever else you already do is a good idea. While using alot of them is a bad idea.