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Thread: No leaks but still losing water; is this possible?

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    No leaks but still losing water; is this possible?

    Hi everyone;

    I have no clue where to begin so I will start with the design of my in-ground vinyl pool liner. The dimensions are: 36' L x 16' W x 5' 9" Deep at Center and 3' Deep at both ends; sports/volleyball pool. I had it for 10 years and it sat empty about 5 years. I had to dig out 10 gallons of dirt out of the bottom of the pool from one part of the wall which caved in. The bottom was dirt but now filled with 2" concrete. The retaining walls are made from plastic or fiberglass. I have two returns, had one but now two main drains, and one skimmer. The pump is 1.5hp with a Hayward 1750 cartridge filter; the pipes are 1.5" PVC. The steps are the fiberglass inserts with liner cut and sealed against steps.

    With that said, I recently replaced the liner; filled it up; and now checking for leaks. After the water reached the arrows on the skimmer a week ago I have been watching the water level drop about 1" to 2" per day. In the past week the water level dropped from arrows to below the bottom of the skimmer faceplate (non-wide mouth) about 6". Just last night the water level for the whole day was right at the screws of the skimmer faceplate; this morning it was at the bottom of the faceplate it dropped 1/2" overnight.

    My question: could the pool be settling or could it be leaking? While the water was at the skimmer faceplate screws I used red food coloring to test for leaks. I dropped food color by all cuts in the liner: pool light, both returns, steps, and skimmer. Of course the skimmer could not be tested but I retightened the screws while the water level was below and now filling it up again to test. I watched the food color spread through the water and cleared. Some of the food color lingered at the steps but not in the location where the seals are. I will test again when the water is at arrows.

    I checked the water level inside the skimmer and it matches the pool water level: I don't have the skimmer float valve which I plan to buy soon.

    Before replacing liner I noticed certain concrete slabs around the topside of the pool has shifted towards the pool meaning it was on the brink of cave-in. I have been checking the slabs for settling as well; haven't notice any movement but I am not taking exact measurements though which I should.

    I have no clue what it could be: the pump has been turned on for a few minutes to check operation but off the rest of the time. My ideas/fears: the issue could be the main drain hose to skimmer because it was my friend who glued it not me or the seals around: skimmer, returns, drains, or light. I am leaning more towards the ground around the pool is settling back to original location but would like other opinions. The food coloring showed no sign of leak. I checked all the walls for floating liner but tight against retaining walls. After the concrete was done: the main drains sat with water for over a week after a flash flood adding about 1' of water; when I installed the liner I had to suck out the water from the drains.

    If I can remember anything else I will update post or reply.

    Thank you in advance.

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    duraleigh's Avatar
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    Re: No leaks but still losing water; is this possible?

    You have a leak. Ground settling is not applicable.

    Since you just replaced the liner, I suspect that the leak is at one of the liner penetrations that had to be made.

    Food coloring tests work but are VERY sensitive and hard for a novice to use effectively.

    If you are out of ideas, I suggest you call a pool pro in for help.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: No leaks but still losing water; is this possible?

    duraleigh, thank you for your reply. I think I fixed the skimmer leak; now onto the other leaks.

    Update:
    Since 1pm today to 5:07pm, there has been a 1/64" drop in water level (about half the arrow width on skimmer faceplate). Tightening the screws on the skimmer has minimized the leak. Tomorrow I will check level before heading off to work; then check after work and will post the results. It seems the water level drops during the night; yesterday morning around 10am the water stayed at the bottom of the skimmer faceplate all day; I checked the water level before going to sleep around 10pm and it was the same; then in the morning I checked the level was at the bottom of the faceplate 1/2" drop in water level. The temps here are 80 degrees in the afternoon; about 42 degrees in the morning and evening; and about 52 degrees the rest of the day.

    I'll keep you updated.
    In-ground vinyl liner: 36' x 16' x 3' to 5' 9" sports pool.
    Concrete bottom of pool; fiberglass/plastic retaining walls; white step insert; concrete slab surrounding pool

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    Re: No leaks but still losing water; is this possible?

    It sounds line your skimmer faceplate.

    Walk away from the pool for a couple of days. Dose the water stop dropping? Your leak is just above that location. I would consider 1/64 changes. Anything less than one half inch doesn't count.

    If the water keeps going down after the lowest return then its the main drain.

    Review the instructions for the hardware that makes up each of your penetrations. Are they installed correctly. Some require two gaskets.
    22k gallon IG pebblefina, Jandy 1.5 HP VS, Jandy CV Cartridge filter, Fafco solar panels, Polaris 360 supply side cleaner, waterfall

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    Richard320's Avatar
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    Re: No leaks but still losing water; is this possible?

    Just out of curiosity, is your backwash valve hard-plumbed into a sewer? A leaking multiport valve couild allow water to escape down the drain and you'll never see it.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Re: No leaks but still losing water; is this possible?

    Quote Originally Posted by gwegan View Post
    Review the instructions for the hardware that makes up each of your penetrations. Are they installed correctly. Some require two gaskets.
    The previous liner had one gasket per each: return, drain, light, stairs, and skimmer.
    In-ground vinyl liner: 36' x 16' x 3' to 5' 9" sports pool.
    Concrete bottom of pool; fiberglass/plastic retaining walls; white step insert; concrete slab surrounding pool

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    Re: No leaks but still losing water; is this possible?

    Quote Originally Posted by Richard320 View Post
    Just out of curiosity, is your backwash valve hard-plumbed into a sewer? A leaking multiport valve couild allow water to escape down the drain and you'll never see it.
    There is no backwash; main drains to skimmer to pump to cartridge filter and then to returns.
    In-ground vinyl liner: 36' x 16' x 3' to 5' 9" sports pool.
    Concrete bottom of pool; fiberglass/plastic retaining walls; white step insert; concrete slab surrounding pool

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