Pool Stain Treat lasts about 30 to 60 days. It's important to keep your Total Alkalinity balanced to keep stains from returning. You can find more information in the Directions tab on the product page and by reviewing the Hamilton Index.
As long as you continue to use Pool Stain Treat every 30 to 60 days and keep your water balanced the stains shouldn't come back. You can find more information in the Directions tab on the product page, and by reviewing the Hamilton Index.