sump. canister. filter

i want to know what you guys think about clay pellets just got into hydroponics as well and have a huge bag left over. i took down my 300 gallon reef tank and wanted my discus and Arowana back in my like after 4 years.(corals sold nice). But with my sump set up, my first chamber wiil be filter...

I have custom made 4'x2'x2' sump with couple campers. And some plumbing. It came with the tank I bought it's too big for my need. I can trade it with fx5 canister. Let me know