I had my phosphates quite high and started using it.
First 2 days no significant changes but then it started to go down to 0.04 and stayed at that level
A.G., like other PO4 removers, once it is exhausted, PO4 will no longer be removed and will begin to creep up. We recommended replacing our media every 3-4 weeks. Testing around the 3rd week is recommended because it will tell you if you can get one more week out of the media.