Just chiming in since I went through the same dilemma and currently running NOPOX/GFO/GAC.
I had really high nitrates and phosphates. I started running GFO and phosphates were being reduced, but water changes weren't helping with high Nitrates. I began dosing NOPOX per instructions and reduced GFO to zero after a few weeks. So, then I had 0 nitrates and high phosphates (I had cyno and it died off spiking phosphates even higher). So, back in the GFO went and then I had the 0 nitrates and 0 phosphates. So, I backed off on NOPOX and GFO and started using Red Sea's Coral Nutrition A & B and feeding heavier to get Nitrate and Phosphate measurable again. So, far so good.
My philosophy, right or wrong, is I use NOPOX to keep Nitrates in check and GFO to keep Phosphates in check. I run a nano with about 11g volume so, I do water changes ( 1-2 gallons) as this really helps with stability for Alk/Calc/pH/trace elements as dosing at small levels is ridiculous (fractions of ml).