We installed our Tigerwood deck last summer. We applied Messmers UV Plus Natural to it last fall. It has faded to a light brown color. There are no stains, algae, mildew, etc. I used some mild dish soap and brush to clean the deck. I used a clean wet paper towel to check to see if it was really clean. The paper towel did turn grey. Is the deck clean enough? Do I need to use the acid type of cleaners and brighteners? Thanks!