If you have phosphate issues, it is most likely caused by something YOU are doing.
Most likely overfeeding or lack of maintenance. I know, you are not "over feeding"... nobody ever does.
Try reducing feeding amounts a little. 25% max at first.
Try more water changes as well.
Adding GFO or anything else is not a solution.
Before dropping money on yet another product to dose your tank with, just try the due diligence. Trust me, you do not need a phos remover in most cases. I did aquarium maintenance for some time, and what I am saying, will work, as I have taken many client tanks from high to low readings.
Once you get it under control manually, you can use GFO or pellets to help maintain.
EVEN if you did just go GFO or something, it is going to take time. Possibly 1-2 months as if you do not change the activity causing the PO4, you are simply fighting it, not controlling.
1) 25% water change - this weekend and again next.
2) reduce feeding up to 25% - watch the fish... if they get skinny, you have gone to far, but generally not going to happen
3) after levels are reduced, use PO4 controlling substance to help keep levels down.
Good luck.