I just ran tests twice today
Here is my start with the alk test and also with the Ca. Notice I start with .83 titration
I did not take my finish with the alk titration but with the Ca
My numbers with the tests were
There is some slight variation but close enough. The only way we can get a definitive answer for you is for a water sample to be set to one of us, a lab testing a sample, one of us flies up to you, or a video of you taking a test. The flight is out of the question and a video is the next best thing to see exactly how you are performing the test

. By the way, nice French manicure

. The reason I say we is that
@Anirban @120reefkeeper and I have been working to find an answer for you. BRS put out a video on testing with hobby kits and Red Sea was the most consistent over of saliferts and a electronic tester with a cost of big bucks. Here is a
link to the BRS thread and video yes they are testing nitrates but what I pulled from the video is that the Red Sea test across the board are very consistent.
I have come to the conclusion that Aquaforest does test high and has some inconsistencies between Aquaforest's inserted test results, but the high Mg will not be toxic or cause issues with your system. The rest of the result that I have read on different threads prove that AF reef salt has a consistent high Mg 1550 to 1600+ and alk at an average of 8.35 and an average Ca of 450 and that has been debated and some are working on more results. I can work with a consistent result more than a inconsistency.
As far as your alk running low and your system looks fine I would test again for the next couple of day and find an average and dose the average.
Do not dose to much alk at one time because that will have
bad effects on your system, I try to keep my alk between 8.5 and 8.6. Slowly raise the Alk if the alk need to be raised. Once you get your alk balanced, you system will start eating up the Ca and Mg through absorption into the corals. The more corals you have and the large the corals get the more the system will absorb of all your elements.