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How to test pool water
Run the pump in the morning for 15 minutes.
Aim on getting there before noon, since the day's heat and sunlight affect the chemicals in the water. If the pool's systems were turned off, turn them on and wait at least 15 minutes for the chemicals to disperse.
As long as the systems were kept on for at least 15 minutes, you can collect the sample immediately. Take the sample in the middle of the pool.