Phos-Zorb is a special filtration material great for use in many applications; including canister filters and wet/dry filters & sumps. Phos-Zorb selectively removes phosphate and silicate. Phosphate is a by-product of fish metabolism; decaying organic matter; and is an additive in some water conditioners and filter medias. In saltwater aquariums; excess phosphate lowers the available calcium and magnesium necessary for the growth of hard corals and other invertebrates. Excess phosphates also promotes the growth of unwanted nuisance algae; and can lead to poor coral health and bleaching. Silicates promote the growth of unwanted brown diatom films. For more information on controlling phosphates; please see our article How to Get Rid of Algae and our That Fish Blog post: Phosphates i ½ Invisible Troublemakers in Ponds and Aquariums.