It would be fine to run carbon and rubble in it, however you should just sell it and buy 2 phosban reactors. The fx5 is way too much flow for gfo, you want the water to flow through the reactor slow so it can react properly with the gfo to remove phosphates.
__________________
Always looking for the next best coral...
90g starphire cube/400mhRadium20k/2 XHO/2x27w UV/2x39w T5/ 3 Trulumen led strips
|