HS aqua Bacto Stones is a biologically active filter material of natural origin with an enormous surface area. The material is able to process both aerobic and anaerobic waste products. This creates better water purification, which in the long run drastically reduces algae growth. HS aqua Bacto Stones create a more stable environment for your fish. The material can be used in biological filter installations and external filters for freshwater and seawater aquariums.