I'll try Miz, but please remember, my opinions and interpretations are just that. I have no degree or formal education in any of these areas.
The first chart give you a comparative to NSW at a given pH (locate your 7 dKh across the top and follow the column down to the 1.0 value (NSW) note that the expected pH is 8.2 The second chart shows the ionic balance of CA and ALK. You stated above that your ALK is 7 and Ca ~420. Thats just about what what is to be expected (7 dKH ~ 410 CA.)
CA and ALK are used by corals at about the same rates. This is why both calcium reactors and Kalkwasser are considered "balanced" as they contribute equal amounts of both CA and ALK. Variances come from unbalanced additions of one or the other (varying 2-part dosing or using salt mixes with higher levels of ALK or CA.)
There are reasons why you might want one value to be elevated or depressed. Aquarists practicing carbon dosing typically maintain lower ALK values (~≤9 dKh) to avoid "burning" the tips of SPS
. In low ALK scenarios, it's more difficult for stony corals to uptake calcium from the water, so it's often suggested that higher CA levels be maintained. You might also adjust values to account for elevated CA or ALK levels in your salt mix.
And in case that's not enough to get your head spinning - the ultimate variable is that the corals we keep in our see-through boxes come from diverse environments with varying salinity/temp/CA/ALK/Light and flow levels. As we try and maintain them all in a single environment - the best we can hope for is creating stable
values somewhere in the middle.
How's that for a long answer to a short question?