[rlabriola]

it is called GFO ( granular ferric oxide)..i might have spelled it wrong. 150g does not seem like a lot in the reactor, maybe 2" or so, but it needs room to move around. when you turn up the water, it will start to tumble, this is what you want to keep the media from clogging...never more than 50 gph though...i never liked phospure, because of its aluminum base...this stuff works better