Also, run your pump 24/7 while fighting algae and brush your pool each day. How did your cya gets so high? I suspect you have been using trichlor pucks. If that is the case - no more of them! Just use bleach. You can either do a partial drain to lower your cya to 30-50 or else keep the cya at 100 and just run higher than normal chlorine levels. See the "best guess" table in the sticky at the top of the chlorine forum.