I would say not for GFO..
GFO works best when fluidized.
Even if the reactor has a pump, the water volume thru the reactor likely wouldn't bring the phosphate down in your system..
But, I have never tried this method so I could be way off...
Well.. Seems to me you have a ULNS which is likely what is stunting or killing your corals..
I would try to bring your traits up to 5-20 ppm..
You might be surprised at the results..