I use the biopellet specific aquamaxx reactor on my tank, worked great with reef octopus bio pearls, changed to brs ones and they're not working the same. Don't use a top plate at all, and I also added a sponge underneath the bottom because in this reactor there is a dead spot for water at the bottom where used pellet scum can collect and start turning grey and creating sulfer which isn't good. Make sure you have some kind of ball valve to control flow and try plumbing it with 3/4 tubing vs the 1/2 inch.
I had nitrates over 90ppm and phosphate around 3ppm at one point, make sure neither bottoms out and dose some kind of bacteria to help, I've used fritz 460 and microbacter7