Does it look like the cover of your pool is lower? Is there water on the grass or cement that doesn’t seem to be weather related? If your covered pool loses water in the winter, you probably have a leak. You need to roll back the cover occasionally and check the water level. If it is lower than usual, you should check for leaks and fix them immediately to avoid further damage.
If your pool lost water overnight and it is more than the quarter-inch due to evaporation, you probably have a leak. Evaporation accounts for a minor amount of water lost each day. Losing a half-inch or move overnight indicates a problem.