That unit does not have a built in pump... it is meant to be used inline with some other pump (or canister)...
It is rated for "up to 700 gph", which means it can handle the pressure of your FX5, but that "up to 700 gph" rating has nothing to do with the effectiveness of the unit...
Pushing 500~600 gph through this 15W UV light (which is what an FX5 will do) will allow the UV light to kill algae and somewhat clarify the water. It will do nothing to inhibit parasites.
If you want the full benefit of this UV unit, I suggest placing a T fitting in the FX5's return line and using ball valves to control the flow rate through the UV to 150 gph. That is 10 gph per 1W of UV strength. This will allow the UV to kill algae, fungus, parasites, clarify water to it's full cpability and any/all other benefits the UV may have to offer.
