GGT Footing and Mag Flakes

Has anyone used Mag on their GGT footing? Looking for feedback. I need to reduce watering and would like to prevent freezing. 20x60 covered arena with GGT and fine sand. My neighbor has used Mag and likes it but has very different sand and a mix of GGT and Nike. Also MUCH less traffic in her arena. If you have used Mag on GGT please tell me lbs per square foot. Does it keep your footing at 12%+ moisture suggested by GGT? Located in the south so high humidity most of the time. TIA