Liner leak

I've ascertained that my 20,000 gal. in ground (which has had a solid cover on it since last September) is losing 1.0 to 1.5 inches of water a month. I discovered it when I went to turn the pump on in mid-winter because the temps were going below 32 degrees and it couldn't get prime because the water had dropped below the skimmer. I've been monitoring it since. (I live in the south.)

I called a leak detection guy who in the past has come out with his drysuit and tanks and dived under the cover to patch a leak in winter. He said he doesn't really service my area any longer and that an inch or a little more a month probably isn't a leak, but rather evaporation. I expressed my doubts as to this (I just don't recall having to add water routinely when it's covered) and he told me to put out a bucket of water, cover it with a tarp, and I would see it evaporate over time. By the way, I have continuous water tubes holding the cover down with no gaps in between them whatsoever.
I called a local pool place and they want--gasp--$250 to dive under and patch a leak. If an inch to an inch and a half of water loss behind the liner (figure on a monthly basis for this analysis) will not damage my aging liner, I'm thinking of waiting until I can get in the pool myself with my wetsuit in early May and try my luck at finding the leak (assuming there is one) with the food coloring technique.

So with the jury out as to whether it's a leak or not, I guess my question is, will this much water going behind the liner cause irreparable harm to the liner? And, I still don't think it's normal to lose this much water through evaporation each month with a solid cover.

Thanks for any ideas, comments.

Hi Elsie :)
It's kind-o-hard to tell if you have a leak or not. A few quick questions:
1) Have you pumped water off of the cover?
2) Did the pool freeze this winter? (probably not, as you live in the south and only discovered it when you wated some circulation for freeze protection)
3) Is there tree debris on the cover (or worse yet, a bicycle or other similar object)?

If you do have a leak, it's small, 1"+ / month isn't a lot of water in a 20000 gal pool. The amount of damage to the liner depends on whether the floor is being 'washed out'. An old, cold liner doesn't have the 'stretch' to keep it safe.
$250 seems a little expensive for what may not be a leak, also realize that they will be charging you for time spent searching for a leak (though if the $250 includes leak detection time, it might be worth it). There is also the possibility that the plumbing has been compromised, in which case the liner isn't effected.
I'm 'shooting from the hip here'. It is questionable whether or not you have a leak. :( I wish I could help you more, but even in the worst case scenario, you could probably 'limp on' with a patch for a season or two if there is a leak that doesn't get found until you open the pool.
Please keep us 'posted'

Elsie,
1" per month I doubt you would ever find a leak with dye. I had a leak of about 50 GPM (yes, minute) a few years ago and probably lost 10,000 gal before I found and patched the problem. Water table is usually high here and what water leaked out just went somewhere without washing away anything. My slits were at the deep end where the bottom transitions to the walls. I'd just let it go and start a record of accurate loss measurements.
Al

Waste & Poconos,

Thanks both for your comments. I have two automatic pumps on the cover that keep it clear of rainwater at all times. I'm fastidious about keeping the cover clear of debris, as well, mostly because I enjoy looking at an immaculate cover - it's akin to looking at a clean pool (I attach an old pool brush to my extension pole each fall and regularly move the leaves and pinestraw to the edge where I then move it off, ad nauseum). No bicycles. :)

Water never freezes. Pump is not compromised, i.e., no leaks. Underground pipes should also be fine; they're way below sea level and I'm sure intact. Liner's 7-8 years old and very faded, although I understand the integrity of the liner should not be compromised by the wearing of the pattern.

There IS all sorts of debris on the seams on the bottom of the pool. For the life of me I can't figure out where it came from because despite copious amounts of tree debris that comes down fall/winter, nothing can get through those end-to-end water tubes. Except ants. I was wondering if maybe I didn't sprout an ant hill after I covered in early September and that's what I'm seeing, along with maybe a pin-hole leak made by same. I put cover on with 2nd person sailor/accordian style so dirty side did not touch water.

Waste: Don't understand "limp on with a patch for a season or two if there is a leak that doesn't get found until you open the pool." Poconos: that must've been somewhat horrifying - lucky save.

So water CAN evaporate even with a tight lid? Ok, I'll monitor and check in with you down the road. Stuff stops falling from newly budding trees (of which I have hundreds) first week in May and then I uncover.

Thanks guys.

Elsie, sorry I'm a little ~ vague at times

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Waste: Don't understand "limp on with a patch for a season or two if there is a leak that doesn't get found until you open the pool."

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What I meant was that if there is a small leak degrading the bottom, and subsequently causing undo liner stress, any damage done between now and May, when you open the pool and can fully check it out - can probably be fixed for a year+ with a patch before having to replace the liner.

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So water CAN evaporate even with a tight lid? Ok, I'll monitor and check in with you down the road. Stuff stops falling from newly budding trees (of which I have hundreds) first week in May and then I uncover.

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There was a thread about solid covers allowing evaporation http://www.poolforum.com/pf2/showthread.php?t=527 - I was less than credulious on that (but could be wrong :eek: !)

From your 'follow-up' post I strongly! suspect that you have a small hole in your solid cover and that you are pumping out pool water when you 'automaticly' pump off the cover. This would also explain the debris that you see at the seams of your pool - the cover water and the pool water are mixing - and what happens to one is happening to the other. This is the basis for my earlier ?#1. I hope that this is all it is and that you do not have a leak in your liner!!

I totally forgot about the possibility of a cover puncture. A few years back a tropical storm caused by one of the hurricanes put so much debris on the pool cover that very thing happened. I kept pumping water off the cover and more water kept appearing as the pool's water level concurrently diminished! I remember remedying the urgent situation by putting an inflatable under the puncture -- worked like a charm until I took the cover off and could patch.

However, this isn't the case this time. We're in a dry spell for this time of year and there is no moisture on the cover. But I sure appreciate being reminded of this 'always lurking' potential.

I'll let you know how this all turns out.

Completely off topic, I received a pool mag in the mail yesterday. I turned to the page on liners, and on some they offer a 25-year-warranty (not that I would buy through this source; I would buy local w/warranty and have professionally installed). I wonder if that means the newer liners can go that long? Wouldn't that be something!