For reference, in your pool, each gallon of 6% bleach will add 2.6ppm of chlorine and each gallon of 10% will add about 4.3ppm.

Let's do an overnight test on your pool. Go ahead and add both of the gallons of 10% this evening. Wait an hour or so and then test your chlorine. Then, in the morning within 2 hours of sunrise, check the chlorine again. See how much you lose overnight. If you lose more than 1ppm, then you should continue to try and keep the chlorine at shock level which for your pool with CYA of 40 would be 15ppm of chlorine.

When you get to the point where you are not losing more than 1ppm of chlorine overnight and you have no more than 0.5ppm of CC and your water is clear, then I would suggest keeping the chlorine high for one additional day for added insurance and then you can let it drift down. Then, keep it between 3-6 all the time. If you dip lower, you risk problems.