Before I would go adding any mag to your tank, I would first try to increase the salinity preferably to 35. Just by doing that you will see your mag jump up. Just top off with salt water for a bit until you get to the right level.
If you are running a Calcium Reactor, a great product is Zeomag from Korallen Zucht. Its 100% pure Magnesium Granulate and you mix it in at 1/3 ratio with your Aragonite. This will also help keep things at the proper ratios and keep you Alk, Ca, & Mg at proper soluble ratios. Keep in mind other factors such as Ph and Alk determine how much Mg (and Ca) your system will hold without precipitation and Carbonate build up.
lol there goes mike with his mag flakes, I use bright well mag and my mag is 1500 so I can not complain. Try that out and see what happens, but all in all. please try what you think is best
I use Epson salt from target. I dose it with every water change. I put the whole carton into one gallon of RO water. I pour 1/4 of the mixture into my fresh salt mix. Check my mag and dose as needed.
Unfortunately, the swap falls on a bad weekend for me this time so I won't be there. I actually don't normally carry Magflake (Dow) because it's only about 80% magnesium. I have Zeomag 100% Magnesium and also Pelletized Magnesium Chloride which is 98% pure.