Absorbs Ammonia, Nitrite & Nitrate Removes Tannins From Water Improves Water Clarity Purigen is a filter media designed to absorb organic waste such as ammonia, nitrites and nitrates at an incredible rate. When in use, it makes for a crystal clear water column. It is extremely helpful if being used to remove tannins as well. It is not known to remove aquatic fertilizers. Over time, Purigen will darken from white to brown so you can visually tell when it has been exhausted. Many hobbyists won't run a tank without it. The 100ml size comes in it's own pouch so all you do is add it to your filter. Rinse before use. Purigen can be regenerated. As it adsorbs waste, Purigen will change color from a pale blonde to a dark brown, almost black. Once it is exhausted, it can be regenerated with a solution of bleach and water. The bleach will literally “burn off” the organics that have been removed from the tank. Soak in a 1:1 bleach:water solution for 24 hours in a non-metallic container in a well ventilated area and away from children. Use regular 8.25% hypochlorite household bleach (non-scented, no dyes, do not use a splash-less bleach). Rinse well, then soak for 8 hours with a solution containing 4 tablespoons of dechlorinator per cup of water. Rinse well. For freshwater use, soak for 4 hours with a solution containing 2 tablespoons of pH buffer per cup of water. Do not reuse if odor of bleach/chlorine is detectable.