I have used Rowaphos in past tanks as part of my normal maintenance using roughly 9 TBs in a 120 gallon system. My current build is testing at 5 nitrates and 0 phosphates, but I have GHA aggressively taking over the rockwork. How do you determine the starting amount of Rowaphos when you don't know your true starting phosphate values? I assume phosphates aren't truly 0....and even if they were, then using GFO wouldn't cause any issues anyways. It is a SPS tank so I obviously don't want to shock them and cause more issues but I need to get this algae under control.