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Thread: Need help diagnosing potential leak - is this overnight water loss normal?

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    deanchat's Avatar
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    Need help diagnosing potential leak - is this overnight water loss normal?

    Hi Everyone,

    I’m trying to diagnose a potential leak. Symptoms:
    - Water level drops more quickly than expected
    - Area of lawn near pool (basically between pool and pump) stays wet longer than other areas
    - I now pump the well-point after every rainfall beacause the liner corners aren't “sharp” - i.e. some water behind the liner. I used to do it only after a big storm.

    I have bubbles in the pump basket, but that has been going on for longer than the more recent symptoms. The bubbles get worse when the water is less than 65 degrees and also get worse when the filter is dirty. The bubbles are definitely a suction-side leak (that I just can’t find) but it seems like the newer issues may be something else.

    I ran the pump overnight and got a 3/8” water loss over about 14 hours, 7pm to 9am. (Pump running, Autopilot on, water is 67 degrees, air temp was 60 at start dropping to 36 overnight and back up to 60 in morning with most of the time in the 30s and 40s, overnight humidity was 35-95% with most of the time in the 80-95% range). Can night time evaporation can be noticeable if the water temp is 20-30 degrees higher than the air temp?

    In any case, is this normal water loss or does this indicate a return (pressure side) leak?

    Correction: Water loss is 3/16, not 3/8 -- reading a ruler when upside down can be a challenge

    Thanks!
    Dean
    37x16 IG vinyl, about 20K gals
    Pentair FNS 60 DE filter
    3/4 hp Pentair Challenger pump
    1 skimmer, 2 bottom returns + 1 step jet
    AutoPilot Dig 220

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    Re: Need help diagnosing potential leak - is this overnight water loss normal?

    3/16" overnight does not sound like a lot. Depends a lot on the size of the pool.

    Have you tried leaving a bucket of water beside the pool and measuring the loss in it just to compare to your pool loss?
    Concrete (gunite) inground pool and spa (80,000 litres/21,000 gallons)
    Hayward H350 natural gas heater (electronic)
    Goldline Aquarite chlorine generator
    Hayward pumps, Hayward Pro Series sand filter, Goldline valve actuators

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    deanchat's Avatar
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    Re: Need help diagnosing potential leak - is this overnight water loss normal?

    I assumed that overnight loss should be 0 with cool temperature, reasonably high humidity, and no sun. Perhaps my assumption is incorrect.
    37x16 IG vinyl, about 20K gals
    Pentair FNS 60 DE filter
    3/4 hp Pentair Challenger pump
    1 skimmer, 2 bottom returns + 1 step jet
    AutoPilot Dig 220

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    deanchat's Avatar
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    Re: Need help diagnosing potential leak - is this overnight water loss normal?

    Pool lost only 1/16" during the day yesterday (sunny, low 80s, humidity in the 20s). Ran a bucket test overnight with the pump off this time. Air temp in the 50s, humidity 70-80%, water temp 68. No discernible difference between bucket and pool loss (both about 1/16"). Will run a pump on bucket test next.
    37x16 IG vinyl, about 20K gals
    Pentair FNS 60 DE filter
    3/4 hp Pentair Challenger pump
    1 skimmer, 2 bottom returns + 1 step jet
    AutoPilot Dig 220

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    duraleigh's Avatar
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    Re: Need help diagnosing potential leak - is this overnight water loss normal?

    The bucket test should be run in a 24 hour period....not overnight.

    Anything 1/4" loss or less is easily attributable to evaporation.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    deanchat's Avatar
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    Re: Need help diagnosing potential leak - is this overnight water loss normal?

    Quote Originally Posted by duraleigh View Post
    The bucket test should be run in a 24 hour period....not overnight.

    Anything 1/4" loss or less is easily attributable to evaporation.
    Was trying to compare pump on vs. pump off situations. I probably jumped the gun and am doing a regular 24 hour bucket test for a baseline.

    Thanks!
    Dean
    37x16 IG vinyl, about 20K gals
    Pentair FNS 60 DE filter
    3/4 hp Pentair Challenger pump
    1 skimmer, 2 bottom returns + 1 step jet
    AutoPilot Dig 220

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    Re: Need help diagnosing potential leak - is this overnight water loss normal?

    Plug off what you think is leaking and then monitor the water level, if you plug the line that's leaking it will stop draining. Then it's time to find it. A very common place is under the bottom of the skimmer. Look for cracks in your deck, crack around your skimmer could be an indicater.

    Oh ya if you can plug off all your suction lines fill your pump up (if it's above Water level) and see if your water drains down to the pool. You've basically isolated that leak to the volume of water only in the plumbing, so a small leak will show up quickly.


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    deanchat's Avatar
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    Re: Need help diagnosing potential leak - is this overnight water loss normal?

    Okay, multiple bucket tests over the past few days show (within my measurement accuracy) the bucket and pool losing the same amount of water, from 1/16 to 3/16 per day. That doesn't rule out a small leak but it's a good sign. Wet area in the yard must be getting water from somewhere and the pump basket bubbles aren't imaginary. Thanks to Chncdafied for the ideas about how to isolate a potential small leak!

    -Dean
    37x16 IG vinyl, about 20K gals
    Pentair FNS 60 DE filter
    3/4 hp Pentair Challenger pump
    1 skimmer, 2 bottom returns + 1 step jet
    AutoPilot Dig 220

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    Texas Splash's Avatar
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    Re: Need help diagnosing potential leak - is this overnight water loss normal?

    Dean, also keep in mind (if you didn't know already) that "if" that wet area was attributable to the pool and not just underground water movement or drainage, then it would most-likely be from the pressure side because as long as the pump is running, it's unlikely you would lose water from a suction line unless the pump was turned off. If you turn-off the pump, then yes you could lose water from the suction line. While running, it would explain some increased air bubbles or drop in the pump strainer basket. You might also try (if possible) to isolate your returns (skimmer versus drains). Perhaps leave the bottom returns off for a day or so (if possible) and see if that effects the bubbles. Then switch to bottom returns only to see if there's any difference.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
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    deanchat's Avatar
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    Re: Need help diagnosing potential leak - is this overnight water loss normal?

    Thanks TX Splash, my thinking is pretty much along the same lines. I am entertaining the idea the a suction-side leak causes the bubbles when pump is on and could let some water slowly leak when the pump is off. This theory might also explain how I get metal deposits even though my pool is filled with metal-free city water but my sprinkler system uses well water with iron (my idea is that a suction side leak could suck in some iron laden water that was used to water the lawn).

    I can sort of isolate things, my setup is odd... I have a single skimmer which is the only source for the pump/filter. I have no drains. I have two pop-up bottom returns (controlled by a single valve at the pump) and a single step-jet (controlled by a valve). Not sure if I could run the system via step-jet as the only return (too much pressure for a single small return?)

    Thanks!
    Dean
    37x16 IG vinyl, about 20K gals
    Pentair FNS 60 DE filter
    3/4 hp Pentair Challenger pump
    1 skimmer, 2 bottom returns + 1 step jet
    AutoPilot Dig 220

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