Stunted coral growth and the presence of unwanted algae is commonly an indicator of excessive phosphate. Phosphate results from fish waste and while... NT Labs Marine Phosphate Remover permanently removes phosphate to help prevent unwanted algae growth in marine aquariums. Ideally used in conjunction with NT Labs Marine Filter Media Bags - position in a high flow area within a filtration system. Dosage calculator available - see https://www.ntlabs.co.uk/browse-products/indoor/marine/phosphate-remover/ Caution: Do not use in fluidised filters.