What you could do is to stop the magnesium for a few days, see if you can salt load then.
I never salt loaded all these years of iodine, but I have taken some extra salt every day for 7 years or something. There are different ways to do this, the protocol are a little too narrow for me; I would ease it up a little.
That said. In my detox phase I had diarrhea alot, it may be a way for your body to clean the bowels. So, I would focus of the all over symptoms, like energy, generally better?.