New pool owner - help understanding pool leak

[mikee30]

Hi all,
I have an in-ground pool that was installed in the mid/late 80s. It has a vinyl liner and I believe the backing is a black resin/fiberglass type material. There is one skimmer (with two inlets in it) and two return line jets. Previous owner plugged the main drain - not sure why. Pool deck is cement
I am struggling to determine the source of a water leak that is preventing me from starting my pool for the summer.

Here is some history and what I have so far:
Last summer, we had the leak and the local pool specialist believed it was the return lines leaking at the joint right behind the jets. I broke the cement deck behind the jets and we uncovered 1 of the 2 jets was leaking under my cement deck, right at the joint. The repair was done, but the pool was closed for the season. This year, when we opened the pool, we realized we still had the leak as we lose roughly 1 inch of water in 24 hours, only when the filter is running. I ruled out evaporation using the bucket test (and the fact it's 1 inch in 24 hrs!). Another test I did was plugging my jets and two inlets in the skimmer to see if I was losing water from the main drain or liner....absolutely no water was lost. I assumed my return lines wouldn't be the problem (as I assumed the pool repair technician pressure tested them after completed his work) and thought maybe the inlet pulling water from the skimmer was leaking. So I dug my grass behind the skimmer roughly 3-4 feet and ran the pump - skimmer was not leaking, nor the two inlets at the joints connecting them to the skimmer. However, after digging ~4 feet, I did find water! I do see my return lines wrapping around the pool in the area I dug, but the water I found is about 1-2 feet below those lines. Since my skimmer is very close to my main drain, I decided to dig another 4 ft hole in my grass in line with the main drain, but behind the cement deck. Again, I found water....I see the return line hoses (which are not leaking) in that location. Another test I was told to do before a pool technician would come was to remove my backwash line and run the filter in "filter" mode to see if I had water leaking at the filter into the line without knowing - I did this and did not find a leak.

My question is...shouldn't there be some sort of joint connecting the return lines to the main drain somewhere within the area of where the main drain is located (but under the cement deck)? If my deep end is ~8ft, does this mean I need to dig 8ft? I will eventually use a pool technician to locate the leak, however, getting access to one this time of year is going to require a wait of 2 weeks - so I have some time to do more tests on my own. What do you guys suggest I do next? If I am finding water 4ft deep behind my skimmer (which is about 2-3 away from my main drain), what should I look for next?

As for what caused the leak - I believe it happened last year, when the filter was put in a mode other that backwash/filter (my guess is recirculate), with the incorrect skimmer inlet blocked, which caused a pressure on the main drain line that was capped inside the pool.

Any ideas would be greatly appreciated.
Sorry for the long post!

Mike

 

[cowboycasey]

Welcome to TFP

If you are finding water under your skimmer but its not from the skimmer it has to be somewhere at the bottom of the pool.. it may very well be at the main drain but until you block that off you may never know..

were air bubbles in the return coming back to the pool?

 

[duraleigh]

only when the filter is running.

So that tells me you should be searching for this leak on the pressure side of the system. Any wet spots visible?

 

[mikee30]

So that tells me you should be searching for this leak on the pressure side of the system. Any wet spots visible?

Hi - thanks for responding. My filter and pump are located next to each other and I was able to gain access to the first 5 feet of lines running out of these machines. There was no leak present in that area. The only presence of water I found was roughly 4 feet deep next to the pool, under my cement deck. One items I doing really understand is how the main drain line runs and if it is tied to the return lines somewhere. My thinking is that given it is an older pool, maybe there is a joint that connects return lines/main drain lines that cracked or maybe the main drain line itself has some sort of coupler/joint to divert the tubing towards the bottom of the pool?

- - - Updated - - -

Welcome to TFP

If you are finding water under your skimmer but its not from the skimmer it has to be somewhere at the bottom of the pool.. it may very well be at the main drain but until you block that off you may never know..

were air bubbles in the return coming back to the pool?

Hi -thanks for responding. When I shut off the filter and had blocked the return lines, the pool didn't lose any water, so I assumed that the main drain isn't leaking, nor is the vinyl. There are a few bubbles in the return coming back to the pool when I start the filter, but after that, I don't see any visible signs of bubbles.

 

[bp460]

Mikee30,

In regards to your skimmer box, one port should be a suction line that goes directly to the pump and I suspect that the second port leads directly to the main drain and nothing else. This style of main drain works on a basic venturi effect and if functioning properly will slowly draw water up from the main drain at the pool bottom to the skimmer box and then the water will get drawn into the suction port to the pump and filter. There is never direct suction at the main drain in this type of system and in fact it is very safe, but not very efficient at circulating water. It is simply a pipe that runs from the main drain to the skimmer box. It's possible that your leak is somewhere in this line . To determine this, you need to isolate this section of line and ideally pressure test it. First, with your pump running, figure out which port has suction. Use caution and avoid getting a finger or hand sucked in the port... it hurts! A drop of food coloring can be helpful. Then, confirm that the remaining port has no suction and then plug it. If your main drain is already completely sealed at the bottom of the pool, this could fix your leak. If its not sealed, you will have to plug the pipe leading to skimmer box with a threaded or expanding plug. The drain itself might also have a hydrostatic valve... make sure it is not leaking. I hope this makes sense. My pool is setup exactly like yours. It is a very simple plumbing set up but works fine. I had a leak between the skimmer box and main drain in my pool and simply put a threaded plug in my skimmer box and an expanding rubber plug in the main drain, effectively isolating the bad section of pipe. This was 7 years ago... much cheaper and easier than digging up the main drain. In fact, when my pool was built in 1975, I am pretty sure it did not have a skimmer box or main drain... just one suction line in the pool wall and two return lines.

Cheers,

Brad

 

[mikee30]

Mikee30,

In regards to your skimmer box, one port should be a suction line that goes directly to the pump and I suspect that the second port leads directly to the main drain and nothing else. This style of main drain works on a basic venturi effect and if functioning properly will slowly draw water up from the main drain at the pool bottom to the skimmer box and then the water will get drawn into the suction port to the pump and filter. There is never direct suction at the main drain in this type of system and in fact it is very safe, but not very efficient at circulating water. It is simply a pipe that runs from the main drain to the skimmer box. It's possible that your leak is somewhere in this line . To determine this, you need to isolate this section of line and ideally pressure test it. First, with your pump running, figure out which port has suction. Use caution and avoid getting a finger or hand sucked in the port... it hurts! A drop of food coloring can be helpful. Then, confirm that the remaining port has no suction and then plug it. If your main drain is already completely sealed at the bottom of the pool, this could fix your leak. If its not sealed, you will have to plug the pipe leading to skimmer box with a threaded or expanding plug. The drain itself might also have a hydrostatic valve... make sure it is not leaking. I hope this makes sense. My pool is setup exactly like yours. It is a very simple plumbing set up but works fine. I had a leak between the skimmer box and main drain in my pool and simply put a threaded plug in my skimmer box and an expanding rubber plug in the main drain, effectively isolating the bad section of pipe. This was 7 years ago... much cheaper and easier than digging up the main drain. In fact, when my pool was built in 1975, I am pretty sure it did not have a skimmer box or main drain... just one suction line in the pool wall and two return lines.

Cheers,

Brad

Hi Brad,
Thanks for the explanation, makes sense. My main drain is plugged from the previous owner and I put in a plug in the skimmer box hole that is tied to the main drain. What I don't understand is why it leaks only when the pump is on and not when the pump is off? Pool tester person that came didn't have the equipment to test the main drain and instead said my return line was cracked in 2 spots and suggested new lines would be a cheaper fix. Was your pool losing water only when the pump was running?

 

[bp460]

Mikee30,

My concrete pool was losing water from cracks in addition to the broken line leading to the main drain. It did not matter if the pump was running in my situation. I only discovered the broken line by isolating and pressure testing it. The style of main drain on my pool (and I assume yours as well) are difficult to winterize properly. Ideally in cold climates they should be plugged at the pool bottom and the water remaining in the line should be sucked out with a long skinny vac hose throught the port in the skimmer box. The line should then be filled with antifreeze and plugged. I think this step is often skipped or overlooked when winterizing. I assume that was the case with my pool and the previous owners.

Cheers,

Brad