Are you IR or diabetic?
If you are IR, you may not need such a high dose of the Chromium. My naturopath said to start out with the 200mcg with breakfast and see how I do. After a couple weeks I wasn't feeling any difference so I added 200mcg with lunch. After a couple weeks I noticed a slight difference, but I still had the cravings, so I added 200mcg with dinner ... you can see where I'm going here.
For more information on the different kinds of Chromium, check out this web site:
http://www.mendosa.com/chromium.htm
I don't know about the Ionic Magnesium though.