I'm still a newbie, but when I "accidentally" didn't rinse my flourite substrate enough, my tank looked like a bowl of chocolate milk. I bought some Fluval Water Polishing pads. Within 24 hours in my HOB filter, the water was clear. There is also a product called Clarity by Seachem. Since my cloudiness was due to the substrate, it helped. The polishing pads are great, though. If that doesn't work, you obviously have a different problem going on. I've read decaying materials/food will cause cloudiness, as well as not cycling your tank properly. Could be a bacterial bloom. I think water changes are the only thing that helps those along. I'm sure someone will correct me if I'm wrong.