Totally agree... Some of my experience w.r.t water properties...
Poisons (ammonia & nitrite) always 0
Calcium 380 to 450 ppm .... Within that range top or bottom no real noticeable difference
Magnesium 1200 to 1400 ppm..... Again, within that range top or bottom no real noticeable difference
Alkalinity 7 - 11 dKH ... personally I have not seen any benefit with levels higher than 8 dKH regardless of nutrient levels
Nitrate 2 - 10 ppm ... My experience was with a low bio load I had to dose potassium nitrate to get to about 5 ppm... That was good... But even better was I just kept adding fish until the system held 5 ppm without dosing. Bought a potassium test kit and found I was very high > 500 ppm. And that was only after a few months of dosing potassium nitrate. When that came down from water changes and I stopped dosing, everything was noticeably better.
Phosphate??? I never get a reading, even with my Hanna low range colorimeter... But I know it's there at some point. I feed 2x a day and combine frozen and pellet. I tested the water from the frozen food and even diluted it had a pretty good amount of phosphate in it. So basically I just thaw it in some RODI and dump it in, no rinsing. I think that alone adds enough phosphate to keep the corals happy.
There really is a lot of wiggle room in the major water params (excluding salinity) the most important thing is they don't keep fluctuating.
Like I said in my earlier post, lighting is a huge factor... And at least for me the most difficult to find what works. The 2 main factors for lights are spectrum and intensity. I couldn't tell you which is most important, because I think they both are. But with both of those there is still some wiggle room. I think the most common mistake with lightning, especially with LED, is having them too close to the water surface. Well, lets say that was MY biggest mistake. I used a standard AI Classic Rail Kit with legs and set it on my tank. That put the lights 8" AWL. I figured that was fine as I had 4 Hydra 26's and plenty of coverage for a 5' tank. But I wasn't really getting great results. So I threw a couple of 1x3's edge wise under the legs to raise the lights to 11" AWL, at the time I didn't change anything else. You can kinda see the wood blocks in this picture
Within a week I saw noticeable improvement. As much as the wood blocks added "character" to the tank, I wasn't feeling the look. So I got the hanging kit to clean things up a bit.
Anyway, sorry for the long winded post. Hopefully something in here will help you out.