So, my opinion on this, along with my company is there is a fine line of right parameters with SPS and getting the best coloration and best growth. These are two different numbers.
The OP is correct, some will say that you cannot have great growth with low phosphates and high alk and this is true. You will run out of nutrients to feed the flesh and provide carbohydrates to get the coral growing at a need rate. They will not be able to process the calcite foundation elements as they have run out of energy after consuming all of the nutrients available to them. A lot of people will have mixed reviews on this. IF they have mixed reviews lets then talk about what they are spot feeding or broadcast feeding. If you use a coral food and direct feed then you will have the required carbs to process everything. Are you dosing carbs proteins, aminos are anything like that to aid in that production?
Now to counter what I just said about the OP post. A lot of the coral farmers like Top Shelf, living reef, and WWC do run a medium Alk level around 8-9 however, they run a higher nutrient level. This gives the corals a lot of nutrients that they need to have the energy to calcify their structures along with provide food for the tissue. Now running like this will provide extreme growth, however the bad note to this is your corals will loose most of their bright intense colors that you see. Great growth but not the best color.
Once you get the growth you want you will see some growers, frag up their corals and then after a week or two of recovery of the frag they will then move them to another tank to brighten up the colors. This tank has a lower Alk Level around 7-8 and a low nutrient level with really high par. The reason for the high par is to get the zooxanthellae to start reproducing at a high rate, which starts producing extreme colors. So, lets target feed, increase carbs and aminos, and get all of our colors back to being vibrant and amazing looking. Get the flesh big, puffy brightly colored and looking amazing.
So the best of both worlds is running a SPS tank on a mixed tank level, especially if you have other corals. 8-9dkh 400-430 calcium 1350-1410 mag ph 8.15-8.3 phos .05 - .12, Nitrates around 10-15. A lot of people will argue this as everyone has an opinion. My opinion and what we run in our Mixed salts with the addition of our Amino acid/carbohydrate/protein/vitamin/and fatty acid blend along with our high nitrogen food to entice the extra energy the corals need to be able to calcify. These levels are used by most of the aquarist in the industry who keep SPS in their display tanks.
One of the things I would recommend to the OP here is figure out what you are after with your SPS and the rest of the inhabitants in your tank and lets get you to what levels is going to work best for your entire collection of corals.
