OK, so last weekend, purely on a whim, I grabbed a container of carbon and a couple of bags to put it in. Now, I have always known that carbon is used in most filter cartridges and that many people use it in their filters. I never thought I really needed it, I do regular water changes and my water has always looked fine. Well I was wrong!!! I put a bag of carbon into the 2nd tray of my CL Biocube 32 on Saturday and I have to say that I am SUPER impressed. My tank is absolutely sparkling clear now. What an incredible difference!!