Pool is half empty overnight!

megamomo

Member
Jul 16, 2008
16
Pittsburgh, PA
Hi All,

I could use some advice on next steps for my pool losing water.

I was intending to close the pool yesterday for the winter. I had the pump running for the last 2 days. On Saturday, I cleaned it thoroughly, but didn't get time to blow out the lines and put the cover on. On Sunday, I woke up to a half-empty pool. The pool was running overnight that night. I heard it sucking air from the skimmers when I woke up.

Currently, I have this situation:
  • Water is well below skimmers and return jets
  • Water is at the top of the lights
  • Pool has one main drain
  • It is an inground pool with vinyl liner
  • Pool was losing water very quickly with the pump on
  • I marked the water height this morning. Not yet sure if it is steady or just going down slowly with the pump off.
  • Pool is 36K gallons. Can't find where 15-20K gallons disappeared to.

I called the only local leak detection company that I know of, and they said they won't work on outdoor pools again until about April.

Right now, I think it could be any one of the following, but please let me know if I'm missing something here:
  • Main drain - leak at the drain or drain pipe. Two local pool experts I called said that this is very, very rare, so they are saying this is low likelihood.
  • Return lines - Pump could have been sucking water from the main drain, then on returning to the pool, the water is lost through a break in one of the return lines.
  • Lights - there are 2 lights, but I doubt this is the cause since the water drop was fast with the pump on and slow/negligible with the pump off
  • Liner - for same reason as the lights, this doesn't seem likely
  • Multi-port valve - Maybe something broke inside this. I did not see any evidence that the backwash hose dumped tons of water though. Usually the grass and leaves in the yard show obvious signs of being blasted with water. It was raining pretty hard, so maybe the rain hid the usual backwash visible signs. I wish I would have tested the valve before putting the filter away yesterday. Is there a way to debug without hooking everything back up again?

For now, I'll wait to see if the water is continuing to fall and see where it stops. Once (or if) it stops, then what is next? One local pool guy suggested I plug all the piping and re-fill the pool now, but that still means that it could be a pipe or the multi-port valve.

If I decide that next Spring is the time to replace the liner (it is at least 15 years old as far as I know and could be 20-25 years if never before replaced), do I need to have the pool filled up to a certain level over the Winter to hold everything in place?

Thanks!
 

AftonJeeper

Bronze Supporter
May 11, 2017
1,151
Twin Cities, MN
Make sure there is at least 1 foot of water in your shallow end otherwise the liner may shift.

15 years is all a liner should do, if you got more than that you are doing well.

Is your equipment pad below the level of the pool?
What position was your multi port valve in when you noticed the issue?
Did you remove the DE filter and leave the pump running?
 

megamomo

Member
Jul 16, 2008
16
Pittsburgh, PA
The equipment pad is clearly above the pool level. I had the multi-port valve on filter during the day as I was cleaning it. I had backwashed the day before but it had been running for 24-36 hours in filter mode without a problem before it lost water overnight the next night. I removed the filter after the problem to put it away for the winter. I already had the circuit breaker turned off at that point, so it would not have been on with the filter removed or after I had closed any return valves.

I checked the water level again this evening and it is still dropping but certainly much, much slower than when the pump was running. It probably lost 3-4 inches in the last 12 hours.

I expect to replace the liner at this point, but need to still figure out if there is something else wrong. The level isn't below the lights yet, but my simple food-coloring test right at the lights doesn't indicate anything is being lost there. Right now the shallow end probably only has 1 foot of water in it.

If I am replacing the liner in the spring, is it still a problem to leave the pool empty if the water happens to drop much further? I know there can be liner issues by leaving it empty too long, but what else could go wrong if the water is low or empty all winter?
 

JamesW

TFP Expert
Mar 2, 2011
23,290
I suspect that the liner has a hole. Look carefully and you might be able to see it.
 

megamomo

Member
Jul 16, 2008
16
Pittsburgh, PA
Given the big difference in water loss with the pump running vs. not running, I was also assuming that this was a pump driven problem, not a simple gravity problem like a liner hole or a leaking light fixture. I can't think of anything to do at this moment but to wait until it stops receding and then reevaluate.

Can anyone answer the part about leaving it empty over the winter? If the liner is being replaced in the spring could I be creating any additional problems by not figuring out a fix now so that I can keep it full during the winter?
 

JamesW

TFP Expert
Mar 2, 2011
23,290
Once the skimmer went dry, the pump was out of the equation. The pump would lose prime and would not pull from the main drain. Look for a hole in the liner.

Do you have any pictures?
 

megamomo

Member
Jul 16, 2008
16
Pittsburgh, PA
I can get pictures tomorrow. It makes sense that it shouldn't keep pulling from the main drain after going below the skimmers, but when I saw it running with the water below the skimmers and return jets, I could see and hear that it was blasting spurts of some water and mostly air back into the pool through the return jets. It seems it was still pulling some water.
 

Swampwoman

TFP Expert
LifeTime Supporter
Apr 27, 2012
3,835
Grand Rapids, MI
Greeting, megamomo.
I may be misunderstanding the chronology of your steps here.I am utterly confused what you mean by this comment - put it away? Is the filter not attached to your plumbing? With the multiport set to Winterize?
I wish I would have tested the valve before putting the filter away yesterday. Is there a way to debug without hooking everything back up again?

So you cleaned the pool. Lost the water. Blew the lines. Drained equipment. Removed filter. Right?

And are still losing water. But the main drain was blown out and the valves closed?
 

Bandit5

Bronze Supporter
Jul 19, 2014
129
Philadelphia, PA
I've only seen this happen when the multiport valve is accidentally left on waste or backwash after cleaning. A leak would normally take a lot more time to drain that amount of water without a clearly visible hole or liner separation.

If you are still losing water with the pump off I would suspect that the plumbing at the main drain separated. That would not be fun.
 

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megamomo

Member
Jul 16, 2008
16
Pittsburgh, PA
Greeting, megamomo.
I may be misunderstanding the chronology of your steps here.I am utterly confused what you mean by this comment - put it away? Is the filter not attached to your plumbing? With the multiport set to Winterize?


So you cleaned the pool. Lost the water. Blew the lines. Drained equipment. Removed filter. Right?

And are still losing water. But the main drain was blown out and the valves closed?

Cleaned the pool. Lost the water. Blew out the return lines and skimmers since they were now above water line. Did not blow out the main drain yet. Closed all suction and return valves. Set multi-port valve to Closed. Drained equipment. Removed filter. Still losing water but at a clearly slower pace than when pump was on.
 

megamomo

Member
Jul 16, 2008
16
Pittsburgh, PA
Here are some pictures. Overnight the water lowered further to midway down on the lights. Still not clear whether the water has stopped receding or not. One light has been missing for years and it certainly appears that the metal canister that contained the light has rusted. That may have finally broke though it doesn't explain the difference in water loss from pump on vs. pump off. No idea what part of the light canister would rust though.

The other light was found to be leaking about 5 years ago. It was plugged by American Leak Detection. That plug may also have finally failed.

I will continue to wait to see if the water recedes further or it stops here at the lights.

Just a few days ago this pool was full and spotless...now it's this...

IMG_20171107_080046445.jpg
IMG_20171107_080035103.jpg
IMG_20171107_080029446.jpg
IMG_20171107_080007366.jpg
 

JamesW

TFP Expert
Mar 2, 2011
23,290
There's a dark spot below the light to the right that looks suspect. Check that.

Check the entire liner for holes. Brush the leaves out of the way or net them out.
 

tstex

Silver Supporter
Aug 28, 2012
1,888
Houston, TX
Ok, back to serious matters.

First, w that many leaves in your pool, if you have a leak, that could be the reason your water loss rate has slowed down: clogged by leaves.

Next, for you to lose that much water in one night, it had to be mechanically driven via the multiport valve being the culprit and you not noticing it bc you admitted it had rained, therefore the water from pool was hidden by rain. Is your return system set to 100% skimmers, or can you also incorporate the main drain? If so, then your pump pulled water from skimmers, then went to the main drain...if you had lots of leaves around the main drain, then that probably stopped the majority of the water flow back to the pump multi-port valve and adios. [If only skimmers, then you probably exposed a weak portion of the 15-25 yr old v-liner and it split and has continued to leak.]

finally, if you are still losing water, then you could also have a leak in the liner as well, in addition to loss by the pump/mpv But, unless the hole was rather large [and now clogged up w leaves], I find it very difficult for a 36,000 gal pool to lose what looks like to be 2 - 2.5ft of water overnight by gravity only....If so, you should still be able to see water leaking w a hole that leaks that much water from a pool your size.

Next steps:

1. Get all the leaves out immediately and see if you can detect anything
2. where ever the water would discharge via the pump/multiport valve, go to that area and take a 3-5 ft metal rod and see if you can push it into the ground easily. then take it to an area of the yd where only rain would hit and see how far the rod goes in there. If little on the latter, bingo. Discharging that amt of water will for sure make the ground super saturated...hopefully if you have any trees w drip-lines in that area, your FC levels were low...

Post back mega and let us know what you determine.

Best of luck and hope you obtain your answer soon...tstex
 

PoolguyinCT

In The Industry
Jul 21, 2014
3,077
Connecticut
That liner looks fried, as if it's been marinating in vinegar for years (low ph) under skimmer ripples are seen- I would check changes in plane, where walls meet floor etc- a tear in those points can easily drop water at your rate of loss.
 

PoolguyinCT

In The Industry
Jul 21, 2014
3,077
Connecticut
Level sitting at hair below middle of pool light niche, don't know if the loss has continued ... though as always anything that touches water is suspect.
 

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