Hi, Mike and welcome! Glad you found us.

With a cya of 40, you need to be shocking up to 15ppm and try and sustain that reading to clear your pool. In 17K gallon pool, each quart of 6% bleach will raise the cl by just under 1ppm (0.9). So, when you test, add enough bleach to get back up to 15ppm. Try and do this as many times a day as you can; at the very miminum morning and evening but more often is better and will clear the pool faster. When the water clears and you are not losing more than 1ppm of chlorine between sundown and sunup the next morning, then you can let the cl drift down. Then, you'll need to keep it between 3-6 all the time so you won't have another algae bloom. Also, run the pump 24/7 while you are trying to clear it up.

Again, glad to have you on the forum. Hope you'll enjoy being a part of our pool community.