You may be fighting something in the water which is consuming your chlorine.

In your pool, each of those 121-oz jugs will add about 4.5ppm of chlorine. So, if you had 4.6 in there and added 9ppm more, that would put you at 13.6. But, then you report that by 6:40 a.m. the next morning, you were down to 10.6. That is a loss of 3ppm overnight. When you lose more than 1ppm of chlorine overnight, it is a sign that you are fighting something.

What I am going to suggest is that you go ahead and shock the pool up to 20ppm this evening. Then, a couple of hours after you add the bleach, test the FC and the CC (I assume you have a Taylor K2006 kit?) again and make note of the readings. Tomorrow morning, within one hour of sunrise, test FC and CC again and see how much chlorine you lost overnight.

You need to continue to keep your chlorine at shock level until you can go from sundown to sunup without losing more than 1ppm of chlorine AND you have no greater than 0.5ppm of CC.

Let us know in the morning the results of your overnight test.