How do I find and fix a pool leak?

Start by assuming it’s a plumbing leak, not the shell. Confirm the leak with a bucket test: fill a bucket with pool water, set it on the first step, mark water levels inside and outside, run the pump for 24 hours. If the outside water drops more, you have a leak. For plumbing, use a pressure test kit ($30–$80) to pressurize lines to 30–40 PSI; a dropping gauge means a leak. Fix it by digging up the pipe, cutting out the bad section, and coupling in a new piece—or call a pro. For shell leaks, use pool dye (not red—it stains).