Use dye to check return line leaks.

Turn off the pump and let the water go still for a few minutes, then squirt pool dye (or food coloring) directly at the return fitting where the water comes out. If the dye gets sucked into the fitting or follows a crack, you’ve got a leak.

The return line is the pipe that pushes water back into the pool. Leaks usually happen at the fitting where the pipe meets the wall or in the pipe underground. The dye test works because when the pump is off, there’s no pressure pushing water out – instead, a leak will pull dye into the opening.

If you don’t see anything, also check the valve at the equipment pad. Sometimes the leak is there, not in the pool itself. And if you’re not sure it’s a leak vs. evaporation, do the bucket test first: fill a bucket with pool water, mark the water level inside and outside the bucket, wait 24 hours, and compare. If the pool drops more than the bucket, you have a leak.

This method is cheap and takes ten minutes. Just don’t use red dye – it can stain light plaster.