Oase Hel X 13, an advanced biological media designed for BioMaster Aquarium Filters. The Hel X bio media has been redeveloped by Oase engineers to further increase its biological settlement surface area by an additional 13%...giving it is name Hel X 13. Hel X 13 consists of small individual bio mechanical plastic casings which allow beneficial aerobic bacteria to settle and breed inside its unique shape. This helps to biologically break down soluble waste to be filtered out while within the Oase BioMaster. Because of its increased surface area, the bio media allows a greater amount of bacteria to be contained within the same sized filter volume. This gives a more rapid breakdown of food and fish waste in the system giving an all round healthier and cleaner water in the pond. The Hel X 13 has a total surface area of 955m²/m³ (compared to 859m² of the older Hel X) and has a protected surface area of 806m²/m³ (up from 704m²/m³ of the older media) While the Hel X 13 has been designed to work with the Oase BioMaster Aquarium Filters, Pond Filters and Modules, it can be used in Vortex based filters to increase their biological capacity. Specifications 800ml Box.