If you suspect a leak in the pool the first thing you should do is a simple bucket test. This test will verify if water loose from the pool is due to a leak or due to normal evaporation.

Here is the 24-hour do it yourself procedure:

1. Take a 5-gallon bucket (home depot bucket) and fill ¾ of it with water and place it on the pool steps.
2. Mark the water level of the water in the bucket with tape and the then mark the outside water level.
3. Check water level with a ruler after 24 hours of normal pool operation.
4. If water level inside and outside the bucket dropped at the same rate, then the water loss is just evaporation.
5. If there was a greater water loss on the marking outside the bucket, suspect a leak in the pool.

Before performing a bucket-test make sure the pool auto fill is OFF (not all pools have an auto fill), otherwise you will not get accurate results because the pool will keep on filling with water.