Water Purification calculations

I rely on rainwater holding tanks for our household water supply.  Does anyone have an excel template or formula for purifying drinking water? 

Found this on the Internet on a quick search.
Disinfecting Water Using Calcium Hypochlorite – The Provident Prepper

Hi Woofy,
   was it you who posted something about your friend and Ulcerative Colitis quite a few years back?
Im new to the forum and didnt know how else to get a message to you besides through this topic.
maybe you arent even on here anymore?.........

I use MMS at 2 drops/gallon, and it works great.