Good idea doing a partial drain and refill. A lower CYA will make your pool much easier to manage. No more triclor tabs or dichlor shock powder. They are both stabilized and will add CYA. Since this is a concrete pool, once you get the cloudy water cleared up you might want to try using cal-hypo for your source of chlorine for awhile. It is recommnended that concrete pools have a calcium hardness reading between 200-400.