Increasing Mg levels

[Ruth]

I have also heard of people using - I think - dolomite stones - Steve help- in their Calcium Reactor to maintain Mg. I have quite a few SPS corals in both my large aquariums and don't really have to fiddle with it that much and when I do I use the Seachem.
You may want to consider switching salts if that is an option - it might be cheaper in the long run.