Help With Leak

[smthomas7]

I seem to have developed a small leak in my in ground pool and can’t find it. I keep my pool covered with a solar cover, so very little or no evaporation and in the past the pool lost water very slowly due to regular usage when the cover wasn’t on. And it’s been a very dry Spring and no use in early Spring, so I can calculate how much I am losing which is about 36 gallons per day. I pressure tested the suction and return lines and they passed. I didn’t pressure test the main drain line, but I plugged it and isolated at the pump pad which didn’t stop it. I used food coloring to test around all penetrations including removal of the light to check the conduit. Although the leak is small (about 1.5 gallons per hour) I assume I would still be able to see the dye get sucked in?

I started checking the rest of the liner for small holes, but no luck so far. I didn’t dye test the entire liner, but looked for soft spots, water bubbles, etc. What size hole am I likely looking for? With a small leak like this is it going to be a pinhole? Would a company that does leak detection have any better methods or would that be a waste of money? Trying to determine my next steps.

Any advice is appreciated. Thanks.

 

[smthomas7]

I forgot to note…when I opened the pool and removed the return and skimmer plugs it was either full or so close to full that I didn’t notice. However, we also get about 40” of rain per year here in PA, so normal rainfall could have been keeping it full over the winter given the small leak rate.

The salt level stays constant as the water level drops and I have to add some salt when I top off the pool level which indicates it is a leak and verifies it is not evaporation. The amount of salt needed correlates directly with the amount of water added as expected using Poolmath calculator.

I also have a cartridge filter (completely closed piping system), so it’s not leaking out anywhere else in the piping system above ground.

 

[Texas Splash]

Other areas to consider:
- Steps or seams
- Hydrostatic valve in the drain area
- Anywhere in the liner as sometimes owners develop a small tear when brushing.
- Depending on how you did the pressure tests, check the inside threaded areas of the return jets. Sometimes a winter plug or pressure testing plug can cover the effected crack in the threads, but once removed it starts leaking again. That was the situation in my case. A very tiny crack inside the return jet at the back of the threaded area at the 12 O'clock position.