I'm not sure I agree that "every tank is different". In many, if not most respects they are all similar, and most processes are (or should be) subject to the same basic chemistry and biology. Problems arise when we start fiddling with natural chemical or biological processes without understanding or appreciating all of the relative ramifications -- many of which still remain unknown, and most of which are uncontrollable.
I don't have an answer for the OP, but with PO4 levels as high as 0.25 ppm and NO3 at 25-35 ppm, I've never seen slowed growth or color issues with any of the SPS, LPS, or zoanthids in my tanks. When I have reduced PO4 to below 0.05 ppm, everything except the SPS suffered greatly. I do not believe it's necessary to maintain your water at an ideal Redfield ratio (if that was even possible without certain insanity). The corals will use what is available to them in the ratios they want... and they will do as well as they can under the conditions they are in. Having been underwater in some reasonably polluted ocean areas, it is clear that corals of many kinds, including acropora, can grow just fine in very high nutrient environments... and the upper limits appear to be far beyond what any of us should ever see in our tanks. Coral coloring, IME, is much more light-dependent than nutrient-dependent.
In any case, chasing numbers to try to achieve what 'somebody' says are the perfect nutrient levels is a sure road to frustration, pain, and failure.
