With CYA that high, you need to keep your chlorine around 20-25ppm. The biggest mistake most people make when dealing with algae is waiting too long between tests and chlorine additions. When you add chlorine, test it again in four hours, then again every eight hours. The chlorine will be consumed rapidly, and most of it will be gone if you wait longer. When the chlorine drops to zero, the algae starts growing again, and you are back where you started