40G breeder tank with approximately 35G of water. Tank is bare bottom, with frags predominantly Zoa. 1/20th of tank volume is rock and sand in seperate section, along with cheato the size of two softballs, also in a seperate section. Tunze 9004 skimmer, and AquaClear 20. GFO material was housed in a porous bag placed in the bottom of the HOB AquaClear, with the supplied foam on top, with water flow set to maximum. I had a reading of 0.58ppm PO4 on a Hanna phosphate checker, I added approximately 1/2 a cup of BRS GFO product SKU#000602. Within 8 hours the reading was 0.07ppm PO4. Please note this is anecdotal, and is offered as a curiosity, and hopefully helpful. I had been looking for information on how to reduce phosphate, how much GFO to use, how often to replace, but specifics are difficult to come by. I thought this might be helpful to someone looking for similar information as myself.