****, I gotta do your research too (JK)?
From the DFS product: "Suggested Use: For freshwater aquariums and ponds, use 1 tablespoon (Tbsp.) of PhosPure per 50-gallons of water, monthly. For saltwater aquariums or heavily stocked freshwater aquariums or ponds, use 1 Tbsp. per 25-gallons of water, monthly. For reef or freshwater-planted aquariums, use 1 Tbsp. per 20-gallons of water. Monitor phosphate levels with a test kit and maintain levels under 0.05 ppm. Replace media as necessary as phosphate levels begin to rise."
From Holmes-Farley: "Salifert recommends using 250 mL (8.5 ounces) of its product (Phosphate Killer) to treat a 125-250 gallon tank for up to three months. There is, however, nothing wrong with starting with 1/10 that amount to see what happens. While it may be more work, using one ounce and changing it after two weeks may reduce some of the issues that aquarists have observed when changing the media.
Aquarists should also be aware that dropping phosphate to extremely low (i.e., growth limiting) levels may cause undesirable effects that reef aquarists do not typically encounter without using such materials."
So, DFS recommends 1/4 cup per 100 gallons and Salifert 1/2 cup+ per 100 gallons. 2 cups is too much IMO and a waste of expensive GFO but if it is working for you stick with it. If you don't have an accurate Phosphate test kit adding random amounts based on someone else's formula can be dangerous. We're just trying to save Rob's corals.
I did 1/4 cup in my 125 and replaced it every 2 weeks. That was after starting for 2 months with 1/2 that amount. The whole time I monitored the PO4 with a Merck test kit. The problem is you need some PO4 in the system as it is fuel for algae, including symbiotic zoanthellae (or however you spell it) in corals.
