i'm batling mustard algae (brown dust looking deposits bottom of pool and walls) iread other posts and state that chlorine levels need to be about 20 to 25 ppm for chlorine to have an effect on this nasty stuff. i have a test kit that measures clorine, br, and ph, only. cl only goes to 5 or 6. how do i know if i have clorine levels of 20 to 25 ppms'.

not sure how to read this things. sorry for the elementary question and thanks.