I make my own with a development of a recipe I got off a Simple/Frugal site.

1/2 tsp salt
4 dstsp glucose/fructose/sugar
one lemming (squeezed)
made up to 1 litre with water

You can vary the flavouring - sometimes I use pomegramate syrup, orange in season or some left-over juice or soft-drink.
I read something from the UN/UNICEF/WHO years ago that they field tested and recommended for babies in 3rd world etc with stomach upsets . It was the same basic theory- lots of water, a tiny bit of salt and a very little sugar .
As long as you are actually eating in general I think you don't have to worry about minor salts you sweat out. (Unless your riding ultra-distances which I at least am not even contemplating)