To keep your aquarium clean and healthy, you’ve gotta get rid of the bad guys — high phosphate levels. Simplicity 1 lb. GFO Aquarium Water Treatment is your partner in fighting the good fight against these phosphates, which can fuel algae and slow coral growth. Granular ferric oxide (GFO) adsorbs phosphates, which leave your finned friends swimming around in healthy coral and less algae. For best results — and so your fish can live their best life — use this GFO in a media reactor or in a media bag placed in a high-flow area.