lawdog

Coral and fish barn for cheap display corals

Picked Up today.

Output your existing fx6 to a diy pvc canister of bio media and have the fx pushing through this to the return.
Or chemical media etc, depending on the drain/bulkhead size the limitation on gravity fed canister may prevent the fx'is running without issues.

You could conceivably output via a large number of diy cylinders.
I have also seen a series of big blue cartridge filters used so you can run a 50, 20, 5 micron pleated reusable cartridge in a row to polish the water. Another option would be gravity fill a sealed large media canister of diy design and have this feed the fx from the high point.

My 2c