I know what it does. It's not a good idea in a reef tank. If you have live rock, that stuff is a moot point. It doesn't "remove" ammonia and nitrite, it hosts nitrifying bacteria that will convert ammonia and nitrite into nitrate. It's nothing special as far as reefs are concerned. For tanks without rock, it's a good option. It is essentially the same thing as bioballs, but fancier.
