Pool covers and evaporation

ToniMarie

Member
Jul 1, 2020
20
Revere, Massachusetts
So my pool was closed last week and I had told my pool guy about noticing that my pool dropped in August about 1 1/2 inches a week. It was still happening even after draining my pool below the skimmer and jets. He pretty much said it could either be the main drain or behind the light. He wasn't completely convinced of the evaporation process which surprised me a bit considering how much i've read up on evaporation and pools around this time of year. The liner is new and was put in last year. So I checked today and in a week it dropped just 1/2 an inch. Clearly nothing close to what it was doing when it was uncovered (1 1/2 inches), which leads me to believe that i was dealing with mostly evaporation (for at least an inch of it). I guess my general question is, will my mesh green safety pool cover still create 1/2 inch of evaporation in New England this time of year? I have a call in to my pool guy, but I was curious. If it is something, I would want to deal with it prior to the cold weather setting in. Does 1/2 an inch warrant hiring someone to come down and scuba dive to check the areas still under water like the light and main drain?
 

cowboycasey

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TFP Guide
Jul 3, 2013
5,409
Southern OK
evaporation is crazzy isn't it...

a mesh cover will still allow evaporation as the cooler air can get to the warmer water... the only way to know for sure is to use the bucket method to check it... fill the clear bucket to the same level as the pool and mark it.. the next day both the pool and bucket should be at the same exact level.. :)
 

ToniMarie

Member
Jul 1, 2020
20
Revere, Massachusetts
evaporation is crazzy isn't it...

a mesh cover will still allow evaporation as the cooler air can get to the warmer water... the only way to know for sure is to use the bucket method to check it... fill the clear bucket to the same level as the pool and mark it.. the next day both the pool and bucket should be at the same exact level.. :)

So if I attempt the bucket test, do I place the bucket on the stairs and then recover the pool with the mesh cover and check it the next day. I've never performed one on a pool that was closed before. I'm wiling to try, but I want to make sure I do it correctly. It's clearly stopped some of evaporation since last week I lost over an inch and this week it is down to 1/2 an inch. However, that 1/2 inch is just annoying me and I want to get to the bottom of it.
 

DorsalSpine

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Jul 8, 2013
716
Columbus, Ohio
So if I attempt the bucket test, do I place the bucket on the stairs and then recover the pool with the mesh cover and check it the next day. I've never performed one on a pool that was closed before. I'm wiling to try, but I want to make sure I do it correctly. It's clearly stopped some of evaporation since last week I lost over an inch and this week it is down to 1/2 an inch. However, that 1/2 inch is just annoying me and I want to get to the bottom of it.
You want the conditions to be the same for the pool and the bucket. With the bucket on the stairs, the pool water and bucket water will stay the same temp. With both of them covered you should see the same evaporation.
 
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ajw22

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TFP Guide
Jul 21, 2013
24,024
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Sounds like evaporation to me. Read Evaporation of Pool Water - Further Reading and you will see how much the wind adds to evaporation versus water temperature differential. Putting the cover on removes the wind component and your evaporation is mostly due to the difference between the water temperature and cooler nighttime air temperature.
 

ToniMarie

Member
Jul 1, 2020
20
Revere, Massachusetts
Just to update on this, I checked my pool a week later and I've had no water loss. I'm going to give it another week and check again. I think I was just dealing with evaporation at this point, or it might have been associated with my light and just reached the point of the leak and stopped. It wasn't a drastic weekly loss to start with. Hopefully, I am ruling out the main drain since the water loss stopped. I've already ruled out the skimmer and intake lines. Either way, I am going to continue monitoring. There is no reason for me to call a leak detection company right now. I will just monitor it and see what happens. August was a wild month in New England so I could have been dealing with evaporation all along. Evaporation vs. a leak can really drive you bonkers trying to figure it out!!
 

ajw22

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TFP Guide
Jul 21, 2013
24,024
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
I will just monitor it and see what happens. August was a wild month in New England so I could have been dealing with evaporation all along. Evaporation vs. a leak can really drive you bonkers trying to figure it out!!

Thanks for the update. Changing weather can create more evaporation then expected.
 
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