Red or stinging eyes usually come from pH out of range or from combined chlorine, not from normal free chlorine levels.
What to do
- Test pH. Keep it between 7.2 and 7.8. Lower it with muriatic acid or dry acid, raise it with soda ash, and retest after 30 minutes.
- Test combined chlorine (CC). Above 0.5 ppm, run the SLAM method.
- Shower before swimming. Sweat, sunscreen and lotions make combined chlorine.