Hi. So we are currently dealing with some algae, and increasing the chlorine levels seemed to have taken care of it. We have some discolored spots throughout our pool (plastered walls) though, and we don't know how to get rid of it. My husband looked into it and stumbled upon vitamin C, but we want to hear your thoughts first before we start using elbow grease and just rubbing vitamin C on it. I've attached a picture so you can see for yourself. That's just about a 4th of the area. Any suggestions? Thanks so much!