There are three possibilities regarding any water loss and they are as follows:
a.) there may be a problem with the return lines going from the filter back to the pool.
b.) there may be a problem with the suction lines from the skimmers to the filter.
c.) there may be a problem with your liner.
First, perform a Bucket Test to determine whether or not you are actually losing water, based on how much water you lose in a 24 hour period. ¼ to ½ an inch a day is normal, based on the temperatures and heat.
1.) Make sure the pool is filled 1/2 way up the skimmers.
2.) Mark the water level on the liner with a piece of masking tape on which you’ve written the date.
3.) Fill a bucket about 1/2 way with water from the pool and place it on the top step at the shallow end.
4.) Mark the water level in the bucket with a piece of masking tape, also with the date.
5.) Wait 48 hours.
6.) Check any drops in the water levels for both the pool and the bucket.
So the premise is this: if the level in the bucket drops the same amount as in the pool (which is the ideal result), then your pool is evaporating water, as per normal. However, if the water in the pool drops, but there is NO drop in the bucket, you may have another issue that we’ll need to research further.
Of course, any rain introduced into your testing equipment (i.e. pool and bucket) will render your test invalid, and you will have to start the procedure over again.
If the Bucket Test determines that you are losing water, you will then want to determine where you are losing the water. A Pump-On/Pump-Off test can help you determine where the source of the water loss is.
1.) Fill the pool up to normal operating level (½ to ¾ of the way up the skimmer openings).
2.) Take a ruler and measure from the top of the liner (where it fits into the track) down to the water level.
3.) Run the filter for 24 hours and measure again. Record exactly how much water was lost in 24 hours.
4.) Now, you turn the pump off for 24 hours.
5.) Take another measurement to see exactly how much water was lost with the pump off.
6.) If you lose more water with the pump ON: there may be a problem with the return lines going from the filter back to the pool.
If you lose more water with the pump OFF: there may be a problem with the suction lines from the skimmers to the filter.
If we determine either of the above two scenarios, we would suggest that you schedule a pressure test of the lines to determine exactly where the problem is.
If you lose the same amount of water regardless of whether the pump is ON OR OFF, then the problem is most likely in the liner. In this case, we would suggest that you schedule a diver to inspect the pool and repair any holes or tears in the liner.