Natural & Low-Maintenance Nitrate Reduction Efficiently removes nitrate from aquariums Designed to stimulate growth of anaerobic bacteria Nano-ceramic, porous structure that will not degrade over time Can be used directly in sump Lasts approximately 6 months For freshwater and marine aquariums Maxspect Anaerobic-Blocks are desingned using proprietary technology to foster the growth of anaerobic heterotrophic bacteria which reduce nitrate into nitrogen gas, completing the Nitrogen Cycle through denitrification. Each block is comprised of proprietary Nano-Ceramic beads made to create a porous surface and anoxic interior perfectly suited for establishing colonies of Paracoccus denitrificans, various Pseudomonads, and more to aid in aquarium filtration. Recommended Use: Stack two Anaerobic-Blocks horizontally directly in sump, placing a Denitrification Catalyst between the two blocks. The Denitrification Catalyst should be replaced every 2 months, while the blocks themselves will need to be cleaned or replaced roughly every 6 months. Do not replace all of the blocks at the same time. Clean or replace half of the blocks so that sufficient bacterial colonies remain to re-establish themselves after each change. Specifications Package Contents - 2 Anaerobic-Block pieces Dimensions - 3 3/4" x 3 3/4" x 1" Surface Area per Block - 11,033 ft2 Maintenance - Clean or replace every ~6 months Treats - 1,000L / 264 Gallons