water evaporation of 7"+ in 10 days?


Sep 16, 2019
Columbia South Carolina
Hey everybody,
Thanks so much for all your past help. A recap of our pool:
We are new pool owners - it came with the house, we bought in July and we love having it.
type - inground, vinyl liner - liner is probably 5-10(maybe more) years old
Size - 10x20, 5.5' deep at deepest (pushing towards 6 if the pool is really full)
pump - Hayward 1 HP max-flo self priming.
local - central South Carolina - temps daytime high 60's to 70's, lowest about 45 at night (usually 50's). I haven't switched from AC to heat inside.

Extra background information:
3 weeks ago one of the PVC lines from pump to filter developed a slow leak. We could have added ANOTHER coupler to the joints already in the line - there had been about 6 other repairs made to this line... Instead we replace the entire line - no problem, simple. This leak was masking a funner one coming from under the pump. Upon research, this appeared to probably be the drive shaft seal. BTW - not the drive shaft seal. I'll be overhauling the pump entirely because it probably needs it. So, the pool filter has not been running for the last 10 days - because it wasn't the shaft seal and we had to go out of town and the toilet started running and the bathtub faucet started dripping - the bathtub faucet is officially dead to me for the rest of the day. That's a completely different level of entertainment that if anyone wants, I'll be happy to share that fun. IT SHOULD have been SIMPLE. So anyway, back to this travelogue.

The current question:
About 2 weeks ago the temps finally dropped enough to quit using the pool, even with the solar cover being kept on when not in use. 11 days ago, I added water to the pool prior to checking the pump repair. This brought the water level to a little above the 1st step. For the last 10 days the pump has not been running and the solar cover has been in place. The skies have been a mix of sunny and cloudy during the day with some rain. Several days ago, I noticed some evaporation that I was a little surprised by. I had a sick child and other obligations and didn't pay much attention until this morning when I look out and the water level is to the bottom of the second step! Measuring that distance seems to be about 7" maybe a little more.

So here's my question, could this just be evaporation, or is something more sinister at play here?


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TFP Guide
Oct 25, 2015

*** Edit*** Never mind Allen was typing while I was and had a better link...Try the bucket test. Wind can actually increase evaporation more than temperature.



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In The Industry
Apr 1, 2007
Sebring, Florida
1/4 " daily is easily attributable to evaporation. 1/2 " daily MAYBE in the desert.

7" in 10 days is a leak


Sep 16, 2019
Columbia South Carolina
7" is too much for evaporation.

So, evaporation test indeed indicates a leak. 2" in pool versus 1/2" in bucket. Upon reflection, I remember some black rubber pulling away from the edge of the steps. So, I conducted a dye test on either side of the steps. Sorry for picture quality. The pic labeled pool2, shows the gasket/seal/rubber pulling away. There is dye in the pic, but barely visible. The dye seems to disappear around the area of the loose rubber, it doesn't seem to move in an obvious way. Some of the dye injected near there will float to the bottom of the steps. Dye definitely dissipates reasonably quickly. Pic labelled pool1, shows a cloud of dye sitting in the water on the opposite side, not moving (several minutes, not dissipated). Can I assume from this that the black rubber is a seal on the stairs and is the potential source of the leak? Skimmer and jets have been ruled out. If this area is the cause, what options do I have?