Honestly I can give an answer to any of it other than it has Been tested and proven in my system for years. I use Reef Crystals which I may or may not do a water change every month. Sometimes I do and others I will go months. I generally only do a water change if I see something has changed in the system.
I rarely test the water, again unless I see something changing. I have it written down and the last water test was 10/24, so about 6 weeks ago. As stated I tested mag today and it was the same as 6 weeks ago and I haven't done a water change since then.
I can't explain it but my Mag never has fluctuation and I use 100% Kalk+2.
Salinity was right on an well.
I use the same Kalk and experience the same with my magnesium as well. I always test for it but it's always 1350-1380. I do do bi-weekly water changes with red sea pro though.
But I wanted to ask you @Reef Pets, do you find that this kalk takes 24 hours+ for the water to be clear again? That's the only thing I don't like about it.