Hi, you did not say how low the water gets before it stops leaking. That could be important. A hole above the water level should be easy to see visually, very easy to spot and patch. Most of the time the holes are on the bottom. If you are seeing wet spots outside the pool the hole is most likely in the cove area.

As the water gets lower the pressure on the hole decreases and they can easily plug themselves up with a little sand or dirt. As soon as you fill the pool the pressure is back on and dislodges the sand and the leak starts. It happens all the time.

I would do a close examination above the water line. If you don't find anything fill the pool and get it clean. You should then be able to examine the bottom. I was never one to use the dye method, it was always goggles for me. Holes in the cove area are pretty easy to spot.

Dennis