Leak - losing same amount of water with pump on or off

Esand323

Well-known member
Aug 6, 2018
82
Indianapolis
Hi all,

I'm trying to find a leak in my pool. On Saturday, I noticed it started to get lower pretty quick. I did a bucket test, but it was not needed as I clearly had a leak. I'm currently losing about 1.5" of water a day. So sometime between Friday and Saturday a leak started. The pool was unused all week. We did have an algae bloom last week and I brought the chlorine up to shock level. It cleared up mostly but then I decided to add some DE to my sand filter to get some of the dead algae out. I put in 1/4 cup at a time until the pressure raised about 1 PSI. That took about 1.5 cups. The DE worked great and we did it about 3 times with backwashes each time. One time, the pressure did get a bit high. It got to around 20 PSI. The MAX PSI shown on our gauge is 22 PSI. I'm not sure if that could have contributed to a leak. Although, we were doing that on Wednesday and Thursday, so I wouldn't think it was the cause of the leak.

I did notice that we seem to be losing the same amount of water with the pump running as we do when it is off. We had a leak in our return line last year and we lost about 2" inches a day when the pump was running, but only 1/2" when it was off. The leak was only about 1 foot below the surface (although it had no visible wet spots on the surface). When I dug down, I could see that it would shoot out like a fountain when the pump was on, but only seep out when the pump was off. That helps explain the difference between water loss with the pump on vs off. However, since this time I'm losing the same amount of water regardless of the pump being on or off, I'm wondering if it is not a plumbing issue and instead a liner tear. I've scanned the entire bottom of the pool twice and I didn't notice any tears. Although, I'm not entirely sure I would be able to notice it. If we're losing ~400-500 gallons a day, would that be larger than a pinhole? I'm just trying to figure out what exactly it is that I'm looking for.

I also tried a dye test, but I'm not very good at doing it. I tried it on the return line and it seemed like it might have been pulling in there, but it's pretty difficult for me to tell. I went ahead and plugged it to monitor the level. Early indication seems to show that it is still leaking, but I need more time for better accuracy. I used this type of plug.
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Next I will try to plug the skimmer, but I will not be able to plug the main drain.

A couple quick questions.
  1. Would the fact that we are losing the same amount of water, regardless of whether the pump is on or off, indicate that it isn't a pressure side issue? Last year when we had a pressure side leak, we lost much more water when the pump was on.
  2. What size tear would I be looking for in the liner if we are losing 1.5" a day (15x30 oval, 12k gallons). I think it comes out to roughly 400 gallons a day that we are losing.
Thanks in advance!
 

CrystalRiver

Well-known member
Jun 19, 2020
234
Massachusetts
If you want to plug the return to rule in/out a leak in that line, you need to seal the line off from the other ends, too. That means using a shutoff valve, or (depending on your setup) plugging all of the return lines and setting your multiport valve to CLOSED. If you don't, water will just flow in through a different return, or through the filter, even though the pump is off.

A pressure side leak will leak more when the pump is on. A suction side leak will leak less when the pump is on, probably sucking air into the system, though it's not guaranteed that you will see air.

400 gallons a day is more than a quart every minute.
 

Esand323

Well-known member
Aug 6, 2018
82
Indianapolis
Thanks, @CrystalRiver! That is very helpful.

I don't really have a way to plug my main drain. I could probably try to get the top off the cover off with a few breaths, but to be honest I'm a bit nervous about doing that. I was able to change the multiport valve to closed. Is that not enough to prevent water from getting to our return line if the return line is also plugged? We only have one return line.

I don't see any air in the pump, so hopefully it's not a suction side leak. If it were a suction side leak, wouldn't we be losing prime? If it were a tear in the liner, any idea what size it would be? I can't seem to find it if it were there. Not sure if I'm looking for a pinhole or something the size of a quarter.
 

CrystalRiver

Well-known member
Jun 19, 2020
234
Massachusetts
MVP closed and all returns plugged is sufficient to isolate everything after the filter.

Suction side leaks don't always cause loss of prime. I have a suction leak that I've been ignoring (monitoring) for a month, with the pump running 24/7. But, it's a slow leak, not 400 gallons/day. At that rate, you would definitely be able to see air in the pump basket and also shooting back into the pool.
 

Esand323

Well-known member
Aug 6, 2018
82
Indianapolis
I sort of figured I would see something if it were suction side. So far it has eluded me though. I would think that if it were a tear in the bottom of the liner, I would see the liner lift somewhere. Or at the very least, it would be soft in some places. We do have a vermiculite bottom. I also thought about a gasket issue. We only have a skimmer, return, and main drain gasket. The skimmer and return gaskets didn't show anything with the dye test. The main drain is difficult for me to do a dye test on though. I have to hold my breath to get down there and when I put the dye out, the water is too turbulent and the dye just disperses too quickly. Although, with the size of our leak, I would imagine the dye should still pull even if the water was turbulent.
 

Esand323

Well-known member
Aug 6, 2018
82
Indianapolis
If the plug doesn't work, it should drop below the skimmer here shortly. I did do a dye test around the skimmer and didn't notice anything. I feel like it would have pulled the dye if it were leaking there given how much water I'm losing.

I did do some digging this afternoon and I think I found where the leak is, although I'm not sure which pipe. I don't believe it is the skimmer, so either the main drain or the return.

20200726_205841.jpg 20200726_205850.jpg

My pool was build back in the 70s, so they used black poly pipe and seemed to have backfilled with pea gravel. I removed about 20 gallons worth of pea gravel and could see standing water. I don't believe this water is ground water, but I'm not entirely ruling out the possibility (although I would be surprised). Just to see, I did a chlorine test on the water with my TF-100. It showed no chlorine. But maybe the chlorine is removed by ground filtration. I figured it was worth the try though.

I used my shopvac to remove the water, but it just kept coming back about as quick as I could remove it. I kept trying to identify where it was coming from, but no luck. Tried turning the pump on and it didn't seem to do anything different to the water level when it was on vs off. I'd imagine the leak is near though.

I went ahead and left it as is. I'm a bit concerned that the concrete deck may cave in as there is nothing underneath a good portion of it after remove the pea gravel. We are supposed to get some stores tomorrow too.
 

Esand323

Well-known member
Aug 6, 2018
82
Indianapolis
Haha yep! The water level in that hole is staying at a consistent level. When I vacuum it up, it just fills to the same height. So it's making me believe that the leak has got to be right around where that level is at. What makes it difficult is that as you remove some pea gravel, more of it just falls in from the sides. So it makes it difficult to make much progress.
 

markayash

Gold Supporter
Mar 21, 2016
2,373
Marietta Ga
Did you look good around where that pipe goes into the pool?
when they plastered mine this last time I found a gap around the pipe. Never knew if it was leaking water or just cosmetic but filled it in
Good luck and stay safe digging under the concrete!
 

Esand323

Well-known member
Aug 6, 2018
82
Indianapolis
I did check there. I didn't notice anything and no dye pulled there. I'm starting to get a bit skeptical that the leak is actually in the return line. It's possible that I don't have the threaded plug in tight enough. I just did it hand tight. Still seems like the water level is dropping. It's only been in for about 2 hours, but the water level is below my mark a small amount. I'll probably also try plugging the skimmer next just to rule that out. I'm beginning to think it could be the main drain. It's one of the pipes in the picture and the entire bottom is covered by dirt. I'm going to try and expose that pipe a bit more tomorrow and see if it leads anywhere.