swimming pool leak please help?

A little more info would be good here. For starters, if you have a temperature difference of 20 F or more between pool water temperature and night time air temp, you can loose 1/2 an inch per night via evaporation easily if the pool doesn't have a solar cover on at night.

Is this a vinyl liner pool? If so..start checking the liner at the water level you say it dropped to. If the water level did indeed stop dropping at that level there's a good chance you'll find a hole. If you have built in stairs use an expired bottle of your pH reagent as dye and check the stair strips at that height. The liner may have torn away from under the strips. Using the dye is better than removing the strips to have a peek, especially if you don't know what you're doing.

Does this pool have an equalizer line ( concrete or vinyl pool here doesn't matter)? That's a pipe going from the main drain up to the front hole ( closest to the pool) inside the skimmer? Have a peek down your skimmer. See a plug there? No equalizer line so ignore what I'm about to suggest. If you simply see that front hole with no plug then you do have an equalizer. It's possible the line is broken. That hole connects to a pipe that leads under the pool shell and down to the side hole in the main drain. Your skimmer will still fill to the current level of the pool water but it'll be leaking. The fix is to hire a diver to plug the side hole in the main drain and to permanently plug the front hole in the skimmer. The cost of a full repair isn't worth it for what that equalizer line does and your pool will run just fine without it. No..this is not something you can do by holding your breath unless you're a champion free diver. You have two screws to remove, a #9 expandable rubber plug ( or a 1 and 1/2 inch threaded ABS plug) to install and cover replacement to do and you'll need to be weighted down to turn the screwdriver. It's cheaper to get the diver in than to drain the pool to do this ( if concrete) and if it's a vinyl pool...draining is NOT an option unless you want to replace the liner too. The liner will shrink, won't sit back correctly upon refilling and may even rip away from stairs or have a seam failure.

Edit: Two skimmers eh? Almost certainly one will be equipped with an equalizer line. Evaporation won't be your problem, given your location so it will be one of the things I mentioned above. You'll just have to check each one or get a pool tech in.