What could be causing the terrible toe and shin cramps I get ruling out water and potium?

I take potium suplements and drink almost 100 oz of water a day but get toe and shin cramps(charlie horses) so bad at night that the only relief i can get is a hot tub of water. I did have gastric byp surgr in 2002 and never had this problem prior to that. Any ideas why and what I can do about it?