As the weather is heating up, more of us are starting to open up our pools and start swimming again. However, you may notice some stains have built up over the winter that you’d like to take care of before using it again. Algae and other organic stains need to be dealt with using the appropriate chemicals, but for many inorganic stains, there is a natural, cheap solution: ascorbic acid. Not only is ascorbic acid a good quality Vitamin C supplement, it also has chemical properties that allow it to react with the metals that cause those stains so they can be dissolved and then removed from your pool water.
Copper, iron, silver, magnesium, and manganese are the common culprits that cause inorganic stains. To test if a stain is caused by metal or algae, rub some ascorbic acid powder (about 1/3-1/2 cup) on one smaller part of the stain. If the stain lightens, loosens, or disappears completely, it is caused by metal, and ascorbic acid should be effective in treating it.
The next step is to neutralize the chlorine in the pool as otherwise it will react with the ascorbic acid (thus requiring you to use much more to react with and remove the stains). The pH should also be close to neutral (no higher than 7.2); the ascorbic acid will have trouble reacting if the water is too alkaline. During this process, you may wish to add algaecide to your pool water to prevent algae from growing while the chlorine levels are low. Next, turn on the pool filter and add the ascorbic acid. About ½ pound to one full pound should be used for every 10,000 gallons of water. Sprinkle into the water around the perimeter of the pool and let the filter continue to run for about half an hour. If the stains are not completely gone, add more ascorbic acid in the areas that are still stained and let the filter continue to run for another half an hour.
If metal stains are a frequent problem, you may wish to use a metal sequestering agent to remove the dissolved metals completely from the water at this point in the process. After the stains have been removed and the sequestering agent added, the filter should be run for another 24 hours before beginning to rebalance the chlorine and pH levels.
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Byrd, S. (2020). Ascorbic Acid for Pools: What You Need to Know. H2ouse. Retrieved May 5, 2021 from https://www.h2ouse.org/ascorbic-acid-for-pools/
Ehowathomechannel. (2013, April 7). Procedure for Ascorbic Acid Treatment for a Pool : Pool Care [Video]. Youtube. https://www.youtube.com/watch?v=ZxgxZ9veq6s
How to Clear and Prevent Metal stains in a Swimming Pool. Thesummerpools.com. Retrieved May 5, 2021 from https://thesummerpools.com/blogs/blog/how-to-clear-and-prevent-metal-stains-in-a-swimming-pool