i bought some of this to clear the silt from my tank during a substrate change (sand), it worked, cleared the water in less than 2 hours, But what wasn't caught by my filters clung to the glass, plants, rocks, and my pleco(looked like a shedding lizard). I'll never use it for that purpose again, but I still find myself using it occasionally after a tank cleaning, when i have stuff flying around the tank. It works by making the particles stick together so they are easier to filter out. I just use 2 capfuls for my 55gal as needed (the recommended dose it 1 capful per 10gal). I still need to clean the glass and filter media(it must be working) a few hours after. The water is crystal clear, comes in handy after a water change if you stir the substrate too much.