Where did the water go?

[cschnurr]

One of our neighbors passed away this summer. Her family knows nothing about pool care, and used a pool company to maintain the pool until the estate is settled. The pool company used a large amount of stabilized chlorine to fight an alge bloom, and her CYA was through the roof. With the help of the great people on this forum, I helped the pool owner (PO) by doing a partial drain/refill which was enoaugh to bring CYA down to about 60ppm. This in conjunction with a SLAM got rid of the algae, but CYA was still higher than recommended.

In mid September, the PO had the pool company close the pool, and I recommended they lower the water as low as possible, so that in spring the refill would dilute the CYA as much as possible. The pool cover is a new plastic sheet supported by water bags around the perimeter. The water bags have two bladders along the length and the PO recalls that some of the water bags only had one of the bladders full of water.

I live in Southern Ontario and the weather has been very inconsistent. We got a couple inches in early November followed by temperatures over 20C (70F), and in mid November had another snow storm. During the 2nd snow storm (about 2 months after closing the pool), the pool cover was pulled into the pool along with the several water bags. When the cover was pulled back, quite a bit of debris went into the water, and the water level was a bit below the floor of the shallow end. The pool company (and I) suspected a leak had drained the pool under the cover and the cover pulled itself into the pool under its own weight because it had no water to support it. Upon inspection, the pool company could not find an obvious tear in the liner and advised the PO to raise the water level to just below the jets, and added some chlorine (stabilized chlorine UGGGH!) to get the clear the water so that a leak detection test involving a scuba diver could be performed. All the plumbing has been blown out and capped and the pool pump is removed so there is no way to get water circulation. Over the past week, the water visibility is clearing up, but the water level has not dropped at all, so we're not even convinced there is a leak. The pool liner is 10 or 11 years old.

Winter is coming with air temperatures dropping below freezing at night.

I am grasping for other theories how the water could have dropped.
The only other two scenarios I could think of was that
a) at close, the water level was dropped much lower and the cover was not floating on the liner at close, and it eventually fell in,
I highly doubt this as I have a photo of the cover installed which doesn't show any sag in the middle.
or
b) I'd expect the pool company closing would not leave less than a foot of water in the shallow end. Could a foot of water evaporate through or around the cover?
As overnight temperatures drop, the water temperature is much warmer than the air temperature, which will promote evaporation. In my own pool, I get a couple inches of evaporation in September.

If it were my pool, I'd let it sit until the spring and figure it out then, but the PO is desperately trying to get this resolved ASAP.

Any help/advice would be greatly appreciated.

 

[1Sammy]

You do not want a 10 year old liner to have low water over the winter. Time of year is bad timing for ya but if a leak can not be found now you have nothing to do except to keep it full of water till the leak can be found. Depending on how it was winterized i would top it off as much as possible to the point of up into the skimmer, again depending on how the skimmer is winterized. Problem with not finding the leak now is in another month or so there will be many inches and maybe a foot of ice in that pool. Once water leaks from below that the ice has to drop and can cause damage to the liner. As to your question, where did the water go, will only 2 options. It was sucked out, or it drained out. If drained they will need to find where , SOON.

 

[cschnurr]

Thanks 1Sammy,
Without a leak test, we can't know if water was sucked out the top, or drained out the bottom.
I don't know if a leak is possible this late in the season. The pool company needs to have the water cleared up before they can do test.
The water is clearing and hopefully a test can be done.

But if a test cannot be done and the pool is left, is the worst case scenario damage requiring a new liner? or do the walls of the pool also get damaged?
I think the PO may just have to live with a new liner in the spring, (as well as any impact on any property sale)

 

[1Sammy]

Depending on ground water and soil type used to backfill, yes the wall could bend in, also if any concrete used can lift.