Could I make up E-lyte electrolyte on my own? Can someone help me make sure I do this properly?

[*GG*]

I have been taking this electrolyte solution for a few months now, and just seem to be needing more and more. It has 178 mg of Sodium, 374 mg of Potassium and 130 mg of Magnesium per serving. There are 40 servings/20 oz bottle.

there is also chloride, phosphate, sulfate, citric acid, sodium benzoate and bicarbonate listed as ingredients. I think the last 2 are preservatives, if not more, so I don't think I would need these compounds to make up my own solution. Not sure of where I could buy pure chemicals online, but I would think I could?

these compounds are not given as mg/serving, so not sure what to make of that?

Here is a website breaking down the ingredients,:

http://www.rockwellnutrition.com/p-bodybio-e-lyte-colloids-balanced-electrolyte-concentrate-20-oz

This is getting very expensive, and I figure I could make it up for much cheaper!!

GG

PS I would just like someone to back up my numbers on how to make up this solution for myself!