TC-M 100 How to return to black screen

I adjusted the GPG hardness setting from 20 to 15 to see if the water can be less slippery/slimy.

I pressed the right arrow button to save my changes to the GPG setting and exit back to the Home Screen. The TC-M would not return to Home Screen. I followed instructions and cycled power by unplugging, waiting 30 sec and plugging unit back into the wall socket.

The unit won’t go back to a blank screen. It alternatively shows the time of day then the version number.

How do I return the system to ready condition and Home Screen?