What does oh mean on a hot tub?

In a hot tub, "OH" typically indicates a low pH condition, which can be harmful to both the spa and its users. It stands for "overheated" or "overheat," signaling that the water temperature has exceeded safe levels. It's essential to address this issue promptly to ensure safe usage and to prevent damage to the hot tub's components. Always refer to the manufacturer's manual for specific troubleshooting steps.