Mysterious major leak

[stephenmilner]

Has anybody any ideas how a solid polypropylene pool can leak 1.25 litres a minute. The level dropped 10 cm in a day and continued to drop until it was about 70 cm from the bottom. That is below the level of the light and the swimjet and obviously the skimmer and circulation jets. There is no bottom drain. A specialist from Albixon checked the light and swimjet for leaks even if the level fell below them. He even removed the roman steps at one end to check for a break in the polypropylene - nothing. As the level drops the leak rate slows but it stops when the pool is half empty. This is an inground pool made from welded polypropylene sheet about 6mm thick on a concrete base and supported by concrete around it. It first started leaking in the winter but the pool is well insulated and the water never freezes. It has a telescopic cover and a floating bubble cover in winter.
There no visible holes, cracks or breaks in the welds, so where is the water going? Surely 6 mm thick polypropylene cannot de porous!

[Teapot]

Hi Stephen and welcome.
This sounds similar to a pool issue on of my customers had several years ago, theirs was a liner pool but listen as a similar thing could occur.
In this case the liner had a hole at the wall floor corner. The water would however stop leaking with a 1/3rd of the water still in the pool, like you way under any fitting.
What actually happens is as the water level lowers the pressure on the pool walls reduces and any hole, poor weld etc closes.

I don't know where in the world you are located but try to find a pool engineer with an Anderson Leak trac, that will with more water in the pool accurately locate the leak in a few minutes. That's the tool I used to locate the leak in the liner pool that was almost 1.5 feet under the line where the water stopped leaking.

Good luck and please let us know how you get on. It's the first polyprop pool I have heard of having an issue but a tiny gap in a weld is easily understandable, It's under warranty?

[stephenmilner]

I'm in France and the pool is from Albixon in Prague CZ. It's not under warranty unfortunately. We refilled it recently after emptying and cleaning as the remaining water had gone green in June's heatwave. It dropped 10 cm in 24 hours, then 5cms and this evening another 4 cms. About another 10 cms and it will have reached the stabilisation point. The welds between the floor and the wall looks fine as do the welds across the floor. It's made from 150 cm wide PP sheet. I've searched for a leak with fluoresceine at the final level but never thought to go to bottom as 70 cm of water still remain. The man from Albixon is coming back as he did not solve the problem last week. I shall follow your suggestion and get him to bring that type of leak tracer. We may have to refill the pool to get a decent flow. At 1.25 litres/minute it must be pissing out somewhere. Thanks for your help.
Stephen

[Teapot]

Hi Stephen,
Yes you will need to at least partially re fill to open up the leak. If your Albixon man cannot find the LeakTrac I would suggest Detection de Fuites 04 74 08 50 50 www.ocedis.com
They will find it with the LeakTrac or hydrophone, as you say a leak of that magnitude should be easy to locate. Sorry not over in france at the moment but being based near Tours it could be some way from you.
Keep in touch, very interested to hear the follow up.

[stephenmilner]

How right you were. The man from Albixon has dismantled the steps and found that the vertical welds for the bottom step had cracked on both sides.
We have decided to replace the steps by a stainless steel ladder as rewelding the PPL steps would further weaken the walls. We probably will not use the pool this year as by the time the water is warm enough it will be too late in the season. However Lake Geneva is close by and the water is about 24 C. Thanks for your advice.

[Teapot]

Glad to have helped Stephen, if you get to take some photos I would be interested to see them.
All the best!

[stephenmilner]

The repair man. from Albixon cleaned out the cracks, welded some PPL into them and double welded a large patch over the whole area. So hopefully all will be OK. Here are the photos. The Alps are still a seismic area and maybe the cracks were caused by a slight earthquake.