How do you check for leaks in an inground pool?

Answer

I had a leak with a new pool and they could not find it.

Finally hired a company called "Leak Locator" and they use equipment like a sonar.

They put a listening instrument in the pool and walked around. they heard the "hissing"sound of the water being sucked out. Within two minutes the person found the two small leaks and sealed them.... Cost me ~ $225.

Answer

get someone that can scuba dive to look around for visible tears/cracks. diver will take a dye substance (food coloring for example) and squeeze it near the suspected area. if it gets visibly sucked into the tear/crack, you've located a problem spot.

Answer

Before you hire a professional leak locator see if you can deduce where you might be losing water. Abnormally high chlorine levels can cause pipes and plastic weir skimmers to crack and leak. (Does the water level fall below the water outlet ports in the pool?) Abnormally low calcium hardness levels can cause paint to chip by leaching calcium from grout and concrete which may enable water to permeate the pool walls or floor. You can also pressure test the circulation pipes to rule that possibility out (don't overdo it with the pressure). You may have recently noticed a sudden change in your pressure gauges which might indicate a compromised circulation pipe. You may notice signs of settling or cracking in deck areas or building foundations which may indicate settling due to water leaks.