I'd be scared because of past mishaps with putting anything inline with an FX5. Notorious for blowing the motor once any sort of back pressure is applied to it. Could work the same way with speeding it up too.
I have 2 and only use them for what they are, and I would personally never modify it. I'm actually under what I should require with my 125 and 120. I have single 300w heaters on both. I get 1-3 degree fluxes in winter time because my doors are open, being in florida it still gets to 80 degrees before AC goes back on, and .5-1.5 in the summer times when the AC is on all the time.
I put a DIY spraybar on my FX5, and the output was ridiculously strong compared to the normal flow. I dont like the large clunky PVC pipe in my aquarium though, so the spraybar was removed only after a short time.
If a flow accelerator could be added to the output of the FX5, with increased flow then that would be something I'd be willing to try...Just dont wanna spend the $15-20 to experiment.
