Aim for 2–3 ppm free chlorine.

Between 1 and 3 parts per million, with 2–3 being ideal. That’s the sweet spot for killing bacteria without irritating skin or eyes.

Lower than 1 ppm and you’re basically swimming in a petri dish. Higher than 4 ppm and you start smelling like a public pool — that strong chlorine smell actually means the chlorine is breaking down contaminants, not that it’s too clean. Also, if you have stabilizer (cyanuric acid) in the water, your chlorine is less effective, so you may need to keep it on the higher end. But for a typical residential pool with CYA around 30–50 ppm, 2–3 ppm is where you want to live.

Test strips are cheap. Test twice a week in summer. Future You will appreciate not turning green.