Thank you!Put some in a bag. Rinse it for a min under tap water. Then place it in your sump in a high flow spot. Measure the difference after 2 days then 4 days. This will give you an idea of how much product it takes to reduce it a certain amount. Po4 will get used up naturally as green, brown, red and other stuff starts to grow on your rocks. Dont panic its all in the process. As stated above your tank will go thru a lot of changes before becomming stable.
Good luck with your tank.