When I set up my Pro3 a 100 micron filter cloth was put between the bottom basket of mech and the 2 top baskets of bio. A 50 micron cloth was put where the white Eheim pad would go. The gauge on the float valve was almost at the very top. Now 8 weeks latter it is down one line! Will take it apart tomorrow to see how dirty they are... all in all the water polishing done by these pads is outstanding and to go 8 weeks until cleaning is great!