I'd love to see an UPDATED cost comparison of the different Chlorine sources available. Home Depot's cost of chlorine locally (SF Bay Area) is around $9/gallon (pack of two for ~ $18). I could not believe the price. Last year it was about $5/gallon. Three years ago, I was buying it on sale at Orchard Supply Hardware for $2.50/gallon. Walmart is now selling for $5.46/gallon (10%).