I try to take magnesium citrate every day, but I am not always able to because I've noticed taking it messes with my sodium levels, and I know this because I can feel it when my dehydration gets worse, so I'm always trying to balance my mineral levels manually.
When I do take magnesium, I only take 50mg with a meal, maybe twice a day. Because of my jacked up mineral levels, I don't take more than 100mg of magnesium citrate per day.
I do plan on upping the amount gradually though, bringing all my minerals up. I've been eating tiny amounts of purple dulse too for minerals, and for more salt I've been eating this canned chicken that has only chicken and salt, no additives. Unfortunately my folks haven't been able to find that chicken anymore, so I'm going to be experimenting with Celtic Sea Salt , although I'm concerned about that because I get terrible reactions to any added salts.
As far as getting diarrhea from magnesium, I was getting that too when I first started messing with magnesium, but since I've lowered the amount I take when I do take it, I haven't had any diarrhea from magnesium. I think you should lower the amount and build up gradually, taking into consideration your other minerals.
Also, you should consider getting some magnesium glycinate. It is apparently the best magnesium available right now, the best absorbed, the most bioactive, etc. "Carlson Lab's Chelated Magnesium" is a good one. I have some here but I haven't gotten around to trying it because I'm working through finishing the magnesium citrate I have, and because I haven't had the strength to be experimenting with new items lately, in case of a blood Sugar crash or some other bad reaction.