Question
I have an in-ground pool and was told that putting Clorox® Disinfecting Bleach in the water would help prevent algae during the winter. Is this true, and if so, how much would I need if my pool holds 33,000 gallons of water?
Answer
There’s a protocol when using Clorox® Disinfecting Bleach for swimming pool disinfection to prevent algae growth when a pool is in use: on an ongoing basis, if you super-chlorinate the pool with 6-12 cups bleach per 5,000 gallons of water, in addition to regular chlorination, algae growth can be prevented. How much bleach you add and how often depends on several factors including how much the pool is used, sun exposure, and water quality. It sounds like from your question that since you are getting ready to close your pool for the season, the pool will not be used for awhile. In that case, I would use the high end of the recommended 6-12 cup range, and add 5 bottles (121 oz. size) plus an additional 3 1/2 cups plus an additional 2 tablespoons of Clorox® Disinfecting Bleach to your 33,000 gallon pool.
[Here’s the math, if you are curious: 33,000 gal. x 12 cups/5,000 gal. = 79.2 cups of bleach. To know how many bottles you will need, 79.2 cups X 8 oz./cup = 633.6 oz. needed. The large size bottle of bleach is 121 oz. so divide 633.6/121 to get 5.24 bottles of bleach needed. To convert .24 bottles (again, 121 oz. size bottle) to cups, multiply .24 x 121 oz. to get 29 oz. Remember that 1 cup = 8 oz, so you would need an additional 24 oz. (3 cups) + an additional 5 oz. ( 1/2 cup + 2 tablespoons) in addition to the 5 full 121 oz. bottles. Whew!]
This treatment can be repeated as needed to keep algae growth under control while the pool is closed for the season—keep an eye on the pool and look for any signs of growth before repeating the treatment. Also, if you decide to use the pool after super-chlorinating, you should first use a pool test kit to confirm that the ppm available chlorine in the pool is 3ppm or less.