FX5 use it on my RSM 34G???

[Red Coral Aquariums]

FX5 900 gph with a 2.5 gallon media area.

It could work if you run the return through the RSM's return locline. It would replace the existing pumps.
I would go with LR rubble with a bag of carbon and a bag of either phosphate sponge or nitrate sponge depending on your needs. Definitely 10 - 15 lbs of LR rubble. You would need to rinse the canister out (it has a purging option) every water change and check your media. No sponges or filters.

Just my thoughts hope it helps.
Kevin