Magnesium needs Vit. C.
Do vitamin C with your magnesium.
If you don't, you might get kidney stones. Which aren't nice, at all at all.
That's preferably a lot more than the paltry 60 mg they're touting as the daily required vitamin C intake up here ... try 2-3 grams of vitamin C with your 2 x 1800 mg magnesium citrate a day. (1800 mg magn.citr. delivers 300 mg magnesium.)
Your kidneys will thank you.
I don't know the mechanism behind the kidney stones. If you do, please enlighten me. Thanks!