Apologies if I missed it, but what type of mechanical filtration, if any, are you using? I battled PO4 for a while and then started using filter socks (changing them out every 2-3 days) which drastically helped. I just recently switched from filter socks to a filter roller (Red Sea ReefMat 1200) which is nothing short of awesome - keeps PO4 down in my system without the hassle of changing filter socks. A good combo of mechanical filtration (filter socks changed frequently, filter roller, etc), skimmer and macro algae should be able to keep your PO4 in check at least to some extent. I know it works for some folks, but for me GFO and LC were hard to balance and did more harm than good.