Hi. I had my pool re-plastered (white plaster) 16 months ago. Recently I have noticed a couple darker stains. Not very big, maybe the size of a baseball or golf ball. I am assuming they are organic in nature. Maybe duck poop that was not removed right away? A leaf? It is in the deep end, so I cannot reach it by hand. I have tried to remove it with a wire brush attached to the end of a pole without success. Should I dive down and try to remove by scraping with a pumice stone or a 3" chlorine tablet? Purchase an attachment (about $11) that holds a stick of pumice stone to the end of a pole? Or buy a "Stain Eraser" online for about $25. Do you have any recommendations?