Test it 2 or better yet 3 times today and each time, add enough bleach to get back to a cl level of 15. Keep doing this until your pool clears up and you do not lose more than 1 ppm of chlorine overnight. (Test it in the morning before the sun gets on the pool.) When you reach that point, I would suggest holding it at shock level for one addtional day just for good measure and then you can begin to let the cl level drift back down. Then, to keep from having this happen again, never let your chlorine level drop below 3. Always keep it between 3-6. (Unless your cya level changes. If it does, check the "Best Guess CYA Chart for the required chlorine levels you'll need to keep.)

Actually, you can test more than 3 times per day. The more often you test it and redose it with bleach the faster it will clear up.