Aqua Medic Antiphos Fe GFO 500ml Highly active iron based granulated phosphate and silicate remover for fresh and salt water aquariums to counteract unwanted algae growth. Antiphos Fe (GFO) does not contain aluminium and is completely non toxic to plants and amimals and is very well suited for use in reef aquariums. 500g can treat a normally stocked aquarium for 3-6 months depending on the phosphate load. Antiphos Fe can bind approximately 10g phosphate/ kg. Check the aquarium phosphate level on a regular basis to determine if the media requires replacement.