The best placement for efficiency is in the clear water chamber of your sump (return pump chamber). This way all or most of the organic matter that reduces the efficieny of the phosphate removal media has been removed from the water via mechanical or biological filtration and you are capturing otho and organic phosphate. To help capture and remove more phosphate keep you Magnesium levels around 1350 ppm. If you would like I have a couple document I wrote breaking down reef chemistry that anyone can understand. send me a PM with your email adress and I can shoot it out to you!