Yeah, basically it's just the ingredients they use in roughly 4:1 proportion.
MKP = Monopotassium Phosphate, can buy it very cheap at hydro stores, amazon, ebay, etc.
Epsom salt provides Mag/Sulfur. You can buy it at the drug store or grocery store. I suspect they add this, because potassium is an antagonist to magnesium and vice versa, as per Mulder's chart:
Apply at regular rates (eg. 1-2g per gallon). Right now I'm using 8g MKP and 2g Epsom to make a little more than 10 gallons.