One of the easiest methods to diagnose a pool leak is to use the bucket method test. The Pool Surgeon actually has a really good tutorial on the subject and gives a complete breakdown on how to conduct this test properly but I will summarize their approach which is pretty much industry standard.

1. Fill a 5-gallon bucket halfway with water. Fill the bucket with the same amount of water as the pool. Use a marker or duct tape to mark this level within the bucket.
2. Mark the pool’s water level at the skimmer.
3. Use a piece of tape or a grease pencil to mark the water level.
4. Return to the mark after 24 hours and double-check it.

Your pool should lose no more than a quarter inch per day. If your pool is losing a lot more water than that, there’s a significant chance you have a pool leak.