Stay on top of it. You may have to check it a couple or more times a day and add more bleach to ensure the chlorine levels don't drop. 12-13 is still too low with your CYA level so every time you let it drop below 15, you're going to be playing catch up and all the bleach you've used will have been wasted.
You will also want to test each day just after the sun is off the pool completely and then again in the morning just before the sun hits it to check your overnight CL loss. Ultimately, you want your loss to be .5 or less.