Here's another thought. My good friend Mike Otto preaches, in a loud voice, "All dirt leaks...some just seems to leak less." With that thought in mind, don't be troubled by a slight leak. As long as your water levels stay close to where you want them, you'll be okay. As the post above says, quantify your leak. Depending where you are, evaporation rates this time of year can be deceiving. It can look like you have a serious leak, when you don't. Quantify, then look at choices to rectify.

Teach a man to grow fish...
He can teach to catch fish...