When using granular ferric oxide (GFO) media for phosphate removal, be sure that it’s housed in a reactor and is not allowed to tumble because of high flow through rates. The media, if tumbling to almost any degree, will crumble over time and shed fine particles that will be carried out of the reactor and into the aquarium. This could cause some cloudiness in the tank, and the particles could settle out of the water column onto corals, as well as just about everything else in the aquarium. To keep the media in place, be sure to use a low speed pump, a ball valve to fine tune the flow rates, and plenty of foam material in the reactor to trap wayward particles. If the media does escape the reactor, a good filter sock will do a great job of removing any suspended particles.