I finally found SpaDepot as a source for DiChlor which (I think) is exclusively for SPA/Hot Tubs.  I have a 500 to 600 gallon spa and about 1 level teaspoon per day is approximately what it takes to keep my spa chlorinated for a day.  While I must also watch the alkalinity/Ph as well, normally the DiChlor is all I need on most days.  I had tried chlorine tablets (they suck in spas and are not DiChlor). Now that I have found it at SpaDepot for a reasonble price, I am a "happy camper".  I also bought some hardness increaser and "Alkalinity & PH down" (to try) when I ordered my 2nd DiChlor. Good luck!