I get the same exact same thing..my toes and calves will cramp after playing. When it happens on the court it is usually severe enough to end my time there.
If your mixture lasts long term in the fridge then I will just do that. Sounds like an awesome little concoction to dose during a match.
Please help TT Member BruceD get a wheelchair so he can play tennis again - http://tt.tennis-warehouse.com/showthread.php?t=496820