Be careful when shocking pools with chlorine. If the water changes color when chlorine is added, it is not the chlorine that has the color, it is the chlorine oxidizing metal in the water. Metal will typically precipitate out at a high pH. With high pH chlorine products, like calcium hypo-chlorite or sodium hypo-chlorite, you can precipitate out metals, which can come out on your surface and form a stain.
Different metals have different colors. Iron creates a brown stain; copper creates a blue or black stain; and cyanuric acid and copper create a purple stain.
Once metals cause a stain you can deal with them with various proprietary products on the market. These products will lift the metal off the surface quickly, but it should be kept in mind that it will take much longer for the metal to be removed from the water in the filtration system. You need to keep a sequestering agent in the water so that the metal does not re-deposit on the wall and cause a new stain.
AT YOUR POOLSIDE 