My thoughts on it is that the statement "everyone's tank is different" suggests that there are just certain things at play that we don't understand. At the end of the day, all of these variables go into an equation that equals a certain result. If different people have different results with different alk levels, then there has to be a reason for it. Our tanks are not magic cauldrons where witches brew potions, they're an equation of variables.
As far as nutrients and lighting, I think it's impossible to recommend an exact par level for any coral. The chlorophyll which creates energy has two inputs, which are light and nutrients. They clearly have a relationship, and my theory is that with higher nutrients, you need higher lighting. After all, the chlorophyll needs both in a certain ratio to grow. Jist to make that more complicated, chlorophyll A and B dont use the red and blue spectrum at the same efficiency, so theres another level of balancing that specteum. Overall though, if nutrients or light are missing, then you're going to hit a stall, and possibly reach photo-saturation.
Now how alk works into that, I'm not quite sure. Same as the light and nutrients for chlorophyll, the zooxanthellae needs certain elements to grow as well. Obviously, everything we test for is part of that equation, but my hunch is that alk is the most significant. The other elements don't seem to deplete so quickly as your carbonate (alk), plus it plays a major role in the growth of the coral as well. That's my theory, at least.
