Removes harmful organics, toxic ammonia, heavy metals, all forms of phosphates, and medications after treatment from aquariums. Poly Filter needs no other chemicals, resins, carbon or other additives in freshwater and marine aquarium systems to aid in aquarium filtration. Poly Filter turns color as it absorbs harmful organics, progressing from white to green to brown and then to black, letting you know when it's time to replace. May be cut to any size or shape and also can be rolled into a circular configuration. Poly Filter turns color when removing medications (blue with copper, red with iron, green with ammonia). Will not soften aquarium water or remove trace minerals.