I'm currently in China and am totally unable to buy electrolyte pills (no one sells the stuff here, and no one outside China seems to be willing to ship here). So, I'd to make my own. Seems logical that I should be able to fill gel capsules with oral rehydration salts (ORS, which are readily available here). I'd then simply count the number of capsules I filled with one packet of ORS and then divide the nutritional information by the number of capsules in order to calculate the amount of sodium, potassium, etc. per capsule. On long runs and races, I think I'm aiming for something like 300-400mg sodium (or 800-900 mg sodium chloride) and 100-200 mg potassium per hour. Does this sound about right?