If you are planning to use the phosguard in a bag, I would suggest placing it in a high flow area of the sump. Where does the water come down from your display? Hard to tell where the drain/overflow and return areas are located. Also, do you have any baffles in you sump? For the longest time, I would shove my bags of carbon, phosguard and purigen in between my baffles. Just make sure the bags are secure so they don't accidentally get stuck to any of your pumps trying to draw in water. T Some people will place an egg crate box around the bags or a rack just before the return pump. This will ensure water is being drawn through the media bags before entering the main display. There are definitely a lot of options, especially if you want to DIY. Can you take some more pics of the sump area and how water is fed from the display down to your sump?