The term 'POOL TESTER' can be broken down into two parts: 'POOL' and 'TESTER'. The word 'TOE' is a three letter solution to the crossword. A POOL TESTER is someone who tests the water in swimming pools to make sure it is safe for people to swim in. They check the pH levels, chlorine levels, and other chemical levels to ensure that the POOL is safe and clean. They also inspect the POOL area for any potential hazards or safety issues.