Brown stains in your pool means you have Iron metal component in your water that has been oxidized by chlorine.
To clear the brown stains in your pool, make sure your pH is not more than 7.2 and FC is low at 0ppm to avoid more brown staining, put your pool filter on circulation and add 1 pound ascorbic acid for every 10,000 gallons of water targeting most stains affected areas and the stains will disappear within 24 hours.
After clearing all the stains, before adding any chemical in your water, add initial dose of metal sequestrant like Orendas SC-1000 or metal removers like Proteam Metal Magic to prevent more metal stains. You will need regular treatment(weekly/monthly) of metal sequestrant or metal removers going onwards to control metal stains.
Alternatively, you can use CuLator Ultra PowerPak in your skimmer and/or pump bucket to remove metal compounds before entering your pool and prevent metal stains when you add chlorine.
Finally, measure and balance all your pool chemicals starting with FC and Cyanuric acid, pH and TA, and all other chemicals.
You can find all these mentioned products on Amazon through above links in the same article. If you more details on how to clear and prevent metal stains in your pool or spa, follow this link:https://dengarden.com/swimming-pools/Fixing-Swimmi...