King British Algae Guard is a naturally derived and an eco-friendly product for the control of Algae aquariums. It is produced from organically-grown Barley straw. When algae takes hold in an aquarium, not only is it unsightly, but it can also be lethal to fish as it drastically lowers oxygen levels. Algae can also restrict the growth of beneficial oxygenating plants, thus disturbing the natural balance of the aquarium.