Based on what?
It is not effective at removing po4 unless added way above the recommended levels However it removes some dissolved organic compounds, as do skimmers, which given time, would break down further into other elements, including phosphates. Some activated carbon can actualy reportedly leach phosphates into your water.
I highly doubt op has such a high level of carbon to result in a dramatic change of po4!
but what do I know I am not a Jedi


