To check for a leak, you can do a “Bucket Test”
You may want to do this when the pool is not going to be used for several days.
!) Put water in a bucket to any level
2) Put bucket on top step of pool
3) Mark the water level inside the bucket.
4) Mark the pool water level on the outside of the bucket.
5) Check after 2 -3 days , the water level should have reduced both inside and outside the SAME amount, if there is more reduction of water level on the outside, the pool has a leak.
The best way is to test this
1) with the filter system off,
2) then with the filter system on.
Typically turn the pool sweep off, (so the tail spray does not affect the results)