Jim,
Why don't you do an experiment? Check and adjust your magnesium weekly and see if there is any improvement. This would have to be a long term experiment, say at least three months, to be able to notice if consistently stable magnesium levels have any effect on fading. If nothing else, you will get to know the magnesium uptake in your tank.
Here's the Reef Chemistry Calculator:
http://home.comcast.net/~jdieck1/chem_calc3.html