This is my second leak job where I will have to rely on my XLT30H to find a leak in under ground plumbing. So I am not very experienced at using this devise. I have spent a couple of hours listening to locate the leak, but no luck as yet. This is a typical backyard pool, no spa, PVC plumbing. At 20 PSI with water the return plumbing looses approx. 5lb. in an hour, with air only looses pressure at a slower rate. I have tried various combinations of water/air, but no luck hearing anything. Any suggestions?

Dave
A PT that loses pressure as slowly as you describe is so small as to not cause a significant water loss, and will not be heard. If you are losing a measurable amount in this pool, you may have some other leak source. A leak that small may actually be in your test equipment?
If it is leaking a couple of ideas to think about: try circulating Fix-A-Leak sealant threw the suspected pipe, it works well on pipes with leaks smaller than 1/8" (clearly your leak is much smaller than that)
A PT with Helium and a Helium sniffer might pick up that small a leak, helium molecules are extremely tiny. helium should leak faster threw the small hole and might make enough sound to hear??
When I do a PT, no loss in 5 minutes = PASS, I would have passed the pipe in question based upon the info you gave.
Please follow up with how you make out on this.
Bruce
poolrepairdiver.com

I agree with Bruce. This is a small leak seems like you are chasing a ghost. I would ask yourself and the homeowner, how much water is this pool losing on a daily bases. five pounds in one hour is not going to produce a significant water volume loss in the pool. if this is a true leak its to small for the xlt to pick up, Helium sniffer could pick it up. But i default back to what is the customer seeing. If its not producing a dramatic loss of water in the pool, why bother.

All good points above, so the first question is how much water loss in 24 hrs ? maybe you've over looked the main leak, or when you plug the return your partially covering the leak with the plug. Dye test the return fitting ? I know I get ahead of myself sometimes and over look the obvious.

another great point. sometimes the plug you introduce in the return or any other fitting temporarily covers up the real leak, masking it and there fore its missed. look inside the return fittings and dye test. another good tool to use is the rigid camera. Bruce uses it and has had great success with it.

I think you are all right. If there is a leak that small in the return line under pressure, it probably would not leak when the lines are not under pressue and just flowing freely. I have identified a leak in the skimmer housing and also where there is some exposed gunite. I really appreciate you guys taking your time to help me, thank you very much!