When I first started supplementing magnesium for afib many years ago, I learned that some people "waste" a lot of mag. I've never pursued these, but know I must urinate out a lot because of the high volume I take in and don't get loose stools. That being said, my RBC's are high. Some folks, like Shannon, have done a lot of the IV mag, too.
No great ideas, except to continue to do what you are doing and exploring.
One thought just came to me. Sarah MyHill is a GP in the UK. She advocates nebulizing magnesium. I've never tried it long enough to be able to give a report on whether it better. Here is a search on her site: [
www.google.com]