I'm with wryknow, employ GFO and monitor your levels in your tank. Make sure your prefilters are replaced every 6 months, membrane every 3-5 years, and just watch for the color change on your DI (I typically replace mine every 6-12 months). If you have a TDS meter hooked up, it's helpful to monitor your RO/DI water.
IMO, PO4 level is everything for acro coloration, assuming it's getting adequate flow and light. If your acros are browning out, lower the PO4 and you'll be surprised at how quickly they start coloring up. I aim for 0.03 ppm myself. I understand that PO4 levels may vary in nature as Tim pointed out but as a counterpoint, most of those corals are also getting blasted by natural sunlight that peaks at 6,000 k. I don't necessarily want that yellow of a tank nor do I want the coloration that is seen in nature comparative to the colors of acros we have established in reef tanks. We've come a long way in such a short amount of time regarding SPS tanks. The SPS tanks of former years were lit with yellow 6,500k metal halide bulbs and everything was a shade of yellow in the tank. Now, we have every color under the sun for SPS coloration and we're using more 14,000 k to 20,000 k spectrum bulbs. We've also stripped the phosphates and nitrates and found better colors to show from it.
Now, with the advancement of technology, we find ourselves overstripping the nutrients in our tanks. As our skimmers become more efficient, different methods of carbon dosing are employed, and new products seemingly coming out daily to help us remove nutrients, we find ourselves overdoing the process of removing nutrients. In that, the trend is now moving back towards less antiseptically clean SPS tanks (your barebottom tanks and overly skimmed tanks) to more nutrient rich but heavily exported systems. Feed a lot, and remove a lot too... just don't overtstrip the nutrients!
I still believe 0.03 ppm of phosphate is a good number to aim for regarding SPS coloration... we don't need 0 ppm of phosphate anymore. I used to be a believer of 0 nitrates too but found better colors around 5ppm these days.
I think you are correct in assuming your algae in the tank is biasing your actual phosphate level. I would employ the GFO until the algae stops growing in your system and recedes and then start monitoring your phosphate levels after that point.