As a filter system. Right now my filter system is insufficient so I'm adding one.
if it is to powerful you can displace the flow with a T-juntion. but I don't think you will need to. I have had a fx5 run on a 60g tank. a fx5 is rated to 400g. how do you plan to place them?
I'm gonna do that. If it's too powerful, I might put a T-junction (just like you said) in one of the pumps for it to just move the water up the filter and back to the tank. I need the other one for the tank because I don't have pumps with airstones. Both pumps will pass water to the filter box of course.