Good Night Kim.
Hello Jamie,
Since you're just learning this stuff, I just did a quick calculation on your pool size, current FC, Goal FC, current CYA, and that you are using 10% chlorine.
By my calculations using Pool Math, the 1/2 gallon you added, (which is equal to 64 oz), is not quite enough.
According to Pool Math you need to add 82 ounces to raise the current FC level of 24 to your Goal FC level of 28. (that is 2 quarts (which is a half a gallon) PLUS 2 more cups.
To use Pool Math Calculator
Make sure your gallons at the top where it says SIZE says 16,000,
Make sure your CYA in the Middle Yellow CYA section says 70 on the NOW (1st box),
Make sure your FC is 24 on the NOW (1st box) and 28 on the GOAL and that your % to the right of that says 10%
After you click to Calculate. If you just move your mouse curser over the FC SECTION (top Yellow section) where it says ADD on the 1st line in the top yellow section (that top section is for Liquid chlorine the ones just below it are for Dry chlorine and you won't be using that lol we Hope). The amount needed will appear at the top just above it for you.
Go ahead and Give it a try, and you'll be a wiz at it before you know it.

You might want to go ahead and also add 2 more cups of chlorine to equal your 81 oz too .
I hope this helps. Feel free to holler back if you have any problems, we are all here to help. Have a Wonderful Night.