Also, if you do want to use the bricks or siporax for nitrate reduction, then placing in the chamber where the tank drains to the sump is not good. Flow will be too high. For nitrate reduction the media needs to develop a near-anaerobic section forcing the bacteria to utilize the nitrates for oxygen. With high flow, this zone will not develop--or will not be as large.
Much better to place in a lower flow area of the sump. I use marine pure 4x8 bricks in the lowest flow area of my sump. Works for me.