I have experienced this as well over few rounds of 5-10gm of ph balanced vit C powder. Leg cramps are usually indicative of electrolyte imbalance in body. I haven't figured out what other electrolytes are being flushed out due to high vit C, but I find stopping use of vit C will get rid of my cramps over a few days as body restores the balance.
I do take Zinc, Mag before bed time, which I am sure helps the balance.