I have a 1950's 40,000 gal gunite pool with on two skimmers (bottom drain closed off).

I've been able to make it work until recently when it started losing prime. I can get it going but the water level won't stay up. I had the system checked and was told that there were no leaks in the pump/filter equipment so he said it had to be in my 'old lines'. But if it's the lines from the skimmers how would it be drawing air and breaking the prime? They recommended calling a 'leak detection' company who will come out for $500 and tell me where the leak is.

I just can't see how it could be sucking air from a line that's several feet underground? There shouldn't be a blockage since I've blown out the lines with the shop vac (on blow) and water shoots up out of the skimmers like fountains. Any ideas would be appreciated! Thanks in advance.

Tanny