Came home to find an empty pool (Updated: Diagnosis and cure at end)

Jimbarstow

Member
Jul 1, 2018
19
Oakland ca
We have a 20,000 gal in ground concrete/gunnite pool. Just before I left on sunday, I checked the pool chemistry and everything looked fine. Got back on Thursday and the pool was empty. Bone dry. A couple minor signs of dampness in the meadow below the pool but other than that, no sign of where the water went.

I originally assumed that the main drain pipe broke but it occurred to me that there could be a leak in one of the pipes feeding the jets. The pump would suck the water from the main drain and just pump it to oblivion. The bottom line is that I have no idea where the leak is. Are pool pipes and drains embedded in the concrete or do they just pierce the wall and run along the edge of the concrete?

We're in a rural area of N California wine country and our pool contractor closed up shop and retired. Finding a new contractor is going to be challenging since I suspect figuring out what happened and fixing it is going to require some real expertise. I've got a call into another pool company but I suspect their repair expertise is more in the area of pumps and filters.

Any advice would be appreciated.

At my darkest moment, I could imagine where the only viable option is to demolition the pool (11 years old) and start over.

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Texas Splash

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Jim, I wouldn't go as far as saying all is lost. Yes, plumbing is routed through the gunite briefly before making its way through the ground and path the builder chose back to the equipment pad, so repairs could vary. But first thing's-first .... fill it back up. You don't want to leave that shell open and exposed. The last thing you want are cracks or for the shell to move. Get it full right away. Once full, there are a few things you can do to determine where the leak is coming from, then you'll be able to take action.

I'd start by operating the system in sections. Maybe there was a rupture at the equipment pad? For the plumbing, consider leaving the main drains closed when you start back up and watch to see if water drops. If not, you can assume a drain line is leaking. But if it does leak with the drains closed, you can open the drains and close the skimmer to monitor. If it still leaks, if may be on the pressure side (return jets), and you may already see that by running the system, but at least you'll know. You also have that cleaner, so there's a dedicate water line for that as well. So you have a few things to watch, but that has to be done with the pool full. Stick close and others will help as well.
 

duraleigh

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In The Industry
Apr 1, 2007
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Sebring, Florida
Pretty unusual. Was the pump left on backwash or some configuration of pump running? In other words, was the water pumped out or did it drain out?
 

Texas Splash

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Jim, since you have a cartridge filter, I don't suspect you'll have a multiport valve, but I'd also be suspect of that solar system. Anything is possible I suppose, but with a leak that pronounced, I imagine you should see where it's coming from fairly quickly once the pool is full and you turn the system on again.
 

Jimrahbe

Mod Squad
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Jul 7, 2014
14,647
Bedford, TX
Jim,

It appears to me you have a water feature (waterfall?) that has its own pump and suction grates at the bottom of the pool.. If so, that is the first place I would look.. I suspect that somewhere on the pressure side going to the waterfall you have a large leak.. We just saw one of these a few days ago, where the pump outlet union cracked right at the pump, causing the same issue.

I agree with Pat, you want to fill your pool back up now.. Then troubleshoot the problem..

Please post some pics of your equipment pad.

My gut says this is not going to be a major problem to find...

Thanks,

Jim R.
 
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Jimbarstow

Member
Jul 1, 2018
19
Oakland ca
The solar system is completely separate and isolated and the pool water is heated by a heat exchanger.

There are no water features. This is a very simple design since we wanted the main feature to be the view. There is a booster pump that feeds the cleaner on a separate circuit.

The pool equipment is situation slightly lower than the bottom of the pool. (This was the design of the contractor. I don’t think I would approve it now.). There is no sign of leakage anywhere. The area around the pool is bone dry. The only sign of water is probably 100’ away and mostly lateral. The only explanation I have is that the water was picked up by a French drain which distributes it to the meadow below.
 

Jimbarstow

Member
Jul 1, 2018
19
Oakland ca
Is the main reason for filling it back up to prevent hydrostatic forces for pushing the pool out of the ground? The pool is actually on a slope and very little of it would be considered to be “underground”. Water is precious in CA and I’m reluctant to fill the pool just to have to leak back out.
 

Jimrahbe

Mod Squad
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Jul 7, 2014
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Bedford, TX
Jim,

Unless you just stumble across the problem, the only way to troubleshoot the system is for there to be water in the pool...

I guess you could just add a couple of feet of water in the deep end and see if it leaks.. If not, than your main drain is not the problem and you could run the pump from the main drain input only and see what happens.

Thanks,

Jim R.
 

JamesW

TFP Expert
Mar 2, 2011
16,598
Was the pump pulling water only from the main drains?

If the skimmers were open, they would begin sucking in air and the pump would lose prime.

If the skimmers were open, the water would not go below the equalizers.

If the skimmers were open, the leak would have to be in the main drain line or hydrostat.

If the pump was pulling water only from the main drains, then the leak could be in a return.

Do you have a picture of the equipment?
 

JamesW

TFP Expert
Mar 2, 2011
16,598
If the solar is a separate pump that pulls just from two of the main drains, I would suspect that that's the most likely cause.

Maybe a break in the heat exchanger or the return lines.

If the main pump pulls from skimmers, it's not likely to be involved.
 

Jimbarstow

Member
Jul 1, 2018
19
Oakland ca
There is no hydrostatic valve. When we constructed the pool, they discovered a seam of hydraulic clay underneath. A soils engineer supervised excavation of an enormous amount of dirt then they added back in (essentially) road base compacted every foot or so. The soils engineer was on site supervising the whole time. The concrete forms for the pool where then built on top of that platform. The downhill side was originally exposed but we put in a huge concrete planter to mask it.
I suspect the pool guy saw no need for a hydrostatic valve give the environment.

The soils engineer's verdict was that this pool wasn't going anywhere no matter what.
 

Jimbarstow

Member
Jul 1, 2018
19
Oakland ca
I just talked to 2 pool guys and both said that given the symptom the problem was most likely the main drain and the simple solution is to just abandon it. One is coming next Friday with leak detection equipment.

I had an algae problem in spring of 2018 and solved it with SLAMming and finding out where it hid out. (Behind the lights.) Since then I've kept the chlorine at the high point of the CYA/Cl tables and have absolutely no sign of algae and stable Cl levels.

One anomaly I saw when I pulled the grates over the 4 drains was that the pots all had a lot of slime. With all the flow through the main drain and high Cl levels, how could this be? Could this slime just be residual dead stuff or could it be a sign that perhaps the main drain was never really working?
 

Texas Splash

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One anomaly I saw when I pulled the grates over the 4 drains was that the pots all had a lot of slime. With all the flow through the main drain and high Cl levels, how could this be? Could this slime just be residual dead stuff or could it be a sign that perhaps the main drain was never really working?
Drains can accumulate bio-film over time since drains are one of those dark and untouched places that we generally don't expose or get a brush to. So periodically someone pops the cover off (often times during a SLAM) and is shocked to find a bunch of muck under there. But if the drain(s) are confirmed to be the culprit, no worries. Your pool can operate just fine with the skimmer alone.
 

JamesW

TFP Expert
Mar 2, 2011
16,598
When you looked in the main drains, did they have water in them or were they dry?

Pour water into each one to see if it holds water.

Are all 4 connected or do you have 2 independent sets of two?
 

Pool Clown

In The Industry
Sep 5, 2008
1,995
Silicon Valley, CA
A lot of rural areas require the installation of a hydrant line from the pool for fire suppression. Did you have one installed? They would typically be a 3" or a 4" line. If that line were to fail, you could drain the pool completely within the 4 days that you were gone. However, If you had one of the pool lines fail, i'm not sure that the pool would drain from just gravity in that amount of time, unless it was being pumped. Once you get a few feet of water back in the pool, turn on the equipment and pull water from just the main drain (if your plumbing allows) and see if there was some kind of plumbing failure at the equipment.
 

Jimbarstow

Member
Jul 1, 2018
19
Oakland ca
I got to thinking about why there are 4 drain openings and realized that the pool builder might have dedicated 2 of them to our dry hydrant. (A dry hydrant allows the fire department to pull water from the pool directly.)

I must have some extra karma since the pool leak specialist came today and determined that the leak is from line to the dry hydrant and is completely independent of any other plumbing. He plugged the drains and I've got a water deliver scheduled to refill the pool