P on your Softub stands for a Pressure reading. It is the pressure of air inside the spa that keeps it from collapsing. The optimal settings are between 15-20 psi.
Here is what you should keep in mind when checking P readings:
• Check the pressure once a month or after heavy usage to ensure proper inflation;
• Make sure to adjust if necessary by adding or releasing air with an inflation device;
• If P drops below 10, try adding more air and monitor over time to make sure it doesn’t drop again.