Even magnesium glycinate (a chelated form) is not tolerated well by my sensitive(ish) gut. The only forms I can tolerate are:
1)Jigsaw Health Magnesium w/ SRT (sustained release technology). I hate to spend so much on it but literally nothing else works for me. Still, I do have to take it with food but can take 2-8 per day with no issue.
2)Mg Chloride - ie magnesium oil. No gut issues with it (obviously) but it irritates the heck out of my skin with burning, prickling sensations even when I dilute it or use less.
3)Epsom Salts - absorption, at least for me, doesn't appear to be significant enough but that may be due to frequency...I'm not willing to waste the amount of water required for daily bathing. I take supershort showers most days.
So for me, Jigsaw it is!
Magnesium glycinate (chelate) in an amount totaling 400-600mg elemental Mg, perhaps Albion Minerals' version (sold by Bluebonnet, among others), on a completely empty stomach, before bed... seems to completely solve the diarrhea issue. I've tried several other alternatives (taurate, citramate, citrate, malate, etc.) and the critical issue seems to be using a highly-absorbable chelate, so the Mg doesn't just hang out in the GI tract and pull in water, and doing so when the stomach has been empty for several hours, ideally.
I've been a natural calm user for the past year. I simply followed the directions on the label, which say to start with a very small amount, twice per day and slowly increase the amount you take.
It does take time (maybe 3-4 weeks for me to get up to the dosage that nets you about 86% of the daily RDA; in other words Natural Calm's full daily dosage) and on the way titrating up occasionally you will probably take a bit too much and have to run to the bathroom but just go slow and add teeny amounts and you'll be fine.