Thank you for the info regarding that product. I have Red Sea mag liquid for dosing when testing shows necessity. Will definitely keep an eye on that parameter so I may also maintain the stability there via dosing as/if necessary outside of water changes.
Here's more info from another thread:
The magnesium in kalk+2 is not useful and incredibly misleading. Here I detail how not useful it is:
https://www.reef2reef.com/threads/best-kalk-stirrer-brands-types.225280/
from those who do not care to switch to another thread, here's the short story:
1. Magnesium is not soluble in limewater, so it will just sit on the bottom
2. The amount present in kalk+2 (Brightwell claims 0.15%) is not nearly enough to meet the demand for magnesium based on that amount of calciuma nd alkalintiya dded (which might, however, be adequately met by water changes with a salt mix with plenty of magnesium).
3. The amount of magnesium in kalk+2 is LESS than is present in many bulk brands of calcium hydroxide as an impurity.
I did a calculation in that thread that, even if one ignores basic chemistry and incorrectly assumes all of the magnesium that Brightwell claims to be in the product gets into the tank water, at a dosing of 1% of the tank water volume daily using saturated limewater, the amount of magnesium added per day is too small to be noticed (0.02 ppm per day).