Try the bucket test to determine if water loss is due to evaporation or a leak.
The Bucket Test
The "Bucket Test" will determine if water loss in a pool is due to evaporation or a leak:
- Bring pool water to normal level.
- Fill 5 gallon bucket with pool water about 3-4 inches from top.
- Place bucket on first or second step of pool.
- Mark water level on inside of bucket.
- Shut off pump and mark pool level on outside of bucket.
- Resume normal pump operation. Make sure auto/manual fill valve is off during test.
- After 24 hours, compare the two levels. If the pool water (outside mark) goes down more than the inside water level, there is probably a leak.
In case of rain, repeat the test.
Test is not valid after 24 hours.