A: One Gallon of Citra-Shield Ready-To-Use will cover approximately 200 square feet. Citra-Shield concentrate will cover 1000 square feet when mixed 5 parts water to 1 part Citra-Shield and will cover 2000 square feet when mixed 9 parts water to 1 part Citra-Shield. Coverage will vary based on type of sprayer used to apply product. The removal time typically ranges from 20 to 28 weeks, depending on factors such as the amount of rainfall, the severity and type of the stain, and the concentration of the mixture used (ranging from 5:1 to 9:1). Green algae is usually removed the quickest, typically within 1-3 days, while black algae may take significantly longer to disappear.