Inevo
One thing, my constant word of warning. DO NOT CHASE NUMBERS
Chasing numbers causes most of ones issues. As long as you are within in a acceptable range. LEAVE THEM ALONE. Meaning this: "I want my Alk at 9. Every time I get it to 9 it drops right back to 8. And it seems to stay at 8 with my sup addition. " LEAVE THE DAMN THING ALONE AT 8.
The more and more you try to fix pH or Alk at some number, with Alk buffers the worse it gets. "Bob" can keep his at 9". DOES NOT mean you can. Doing the WC you are doing @ 20-25 % / wk, should help this from not happening. One must remember that when you add sup's, other than Kalk, you are adding other ions not needed, ie., like Sodium, Sulfate, etc. These accumulate over time and cause an off-set in the Ionic-Balance, which shifts the solution Kinetics of the water. You can actually see this at times when adding a Alk buffer. A cloud will form, which will not dissipate quickly, as in a few seconds but may take mins. This makes it very difficult to maintain wanted levels, even NSW levels. 20-25 % WC/ wk or 30 % / month should stop this.
Nitrates 5-10 ppm is a good range = mostly so much gibberish but may be fine for some. NSW or any coral reef is nowhere near that. But does it have any real meaning or merit ? It can, as many have such levels with no issues. It is because the corals have gotten use to them. Probably the biggest reason is many of those corals you get are in high Nitrate, 5-10, and if they are put in a system with low Nitrates they often crash. The same thing ofen happens when you take corals from a low Nitrarte system and put them in a high Nitrate system. Or doing massive WC in a high Nitrate system. The same is true with Phosphate. Such high levels can even make corals grow fast, especially with elevated Alk levels also. But is this a good thing ? For one, the corals Coenosarc can becomes thin and the density and porosity of the Aragonite becomes less dense and more brittle. The makes it easie for the Coensarc to tear and become damaged and infected and makes the corals branches brake easier. In a reef tank this may not be an issue, as reef tanks are not subjected to much wave action or impacting rubble like a coral reef. Each tank and its system is different. So, you have to go by what works best for YOUR TANK NOT BOB's TANK. If everybody followed Bob's methods we would not be much of anywhere in this hobby !
Please stay and do what you are doing, being CONSERVATIVE !