Chasing numbers is not good - for sure. However, if you need to lower P, then GFO is fine if you are smart and slow. Most people mess up because they are chasing, do not understand how to use it or do not understand how the aragonite is both working for, and against, them depending on the levels and goals. This is complicated, for sure, but if you want to be successful, then you have to understand.
More about aragonite binding of phosphate... when you get fresh live rock or sand (from the ocean) is is mostly phosphate free since the reefs are very low levels of phoshate and rock has given up all the phosphate that it has. Early on in a new tank, the rock can bind up all free phosphate in the water and leave your test kit showing VERY low or at zero. This takes a few months, or more, to bind up enough so that there is some left in the water. On a normal tank, this can happen along with the cycle and early phases of the tank and it is no issue since by the time that you are ready to add coral there is enough bound up in the rock to leave a trace for the coral and other inhabitants. In this case, the aragonite can act like a buffer absorbing a bit more in between water changes and releasing some when the water gets too low - this is good and healthy. When people use GFO, LC and Organic Carbon from the start, they do not allow the rock to bind up during the early stages and it has to do it later on. It is good to be patient with a new tank and let nature work.
Dry rock has also thrown a wrench in all of this since it is nearly always bound with some terrestrial phosphate and sometimes it has A LOT. Treatments to remove this in the tank can sometimes strip the water too clean in order to get the rock to release as much P as possible to growth-limit the algae - this is the scenario that you see with VERY low residual P levels, but hair algae all over the rocks. This can grow-limit the corals by denying them building blocks. I used to caution people to avoid dry rock at all costs, since the costs over the first few years of ownership can dwarf the cost of real phosphate-free rock, but without a good current source of real pacific rock, I don't know what to do now.
While I do totally believe that acropora (not so much other corals) do grow and color better with very low, but detectable, building blocks (along with lots of food from the zoox from high quality lighting), I would not recommend this until a tank is REALLY stable - most people on this board might not have a tank old enough to be here which sometimes requires 2-3 years of being set up.
