Keep in mind that the Redfield Ratio is the
uptake ratio of phytoplankton. It is not the ratio in the ocean, nor is it the
uptake ratio of corals. It is a good guideline to use though, just as long as you understand it. Really all the Redfield Ratio is doing is putting in perspective how tiny of an amount of PO4 you need in comparison to NO3.
FWIW, 1.5 ppm NO3 is 50x PO4 at 0.03 ppm. Redfield Ratio is 16x.
The way I see it is that no matter how hard we try to mimic nature, we just can't do it nearly as well, so we use fertilizers (literally haha) to try to supplement the corals. It works in many cases, but not all. It depends what's missing or lacking in your own system. There are examples all over the map of tanks with high nutrients and SWEET Acros, and there are examples of SWEET Acros in immeasurable amounts of nutrients. Everyone's tank is different, and this may not be your magic potion.