I did some research on this a few years back after getting severe leg cramps hiking down from a Mt Washington Climb.

Electrolytes are basically sodium+postassium, so I researched about 15 brands on the market comparing each ones sodium/postassium contents.  From my comparison, a few years ago, camlelbak tablets had the highest concentrations of both.  Some other brands tabs were higher in sodium and not so much potassium, others high in potassium, low in sodium. 

Anyway they have worked for me (and my wife when she started have leg cramps at night for a time).  Put 1 tab in your liter botter, good to go.  good luck

REI member since 1979/retired engineer

REI Member Since 1979 YouTube.com/philreedshikes