For lighter colors, wash the deck with a mild mixture of 5 to 20 parts of water and one part of muriatic acid. (Test a small unobtrusive area first to ensure results are acceptable). Always be careful using muriatic acid and make sure to follow all instructions from chemical supplier. Avoid using muriatic acid on dark colored products as it might alter the color. Choose a cleaner that does not contain muriatic or phosphoric acid for better results.