The inspect cell message is displayed on a timed interval inside your controller. It can be cleared, and will return on a regular basis. To check and clean your cell,

Make sure the pump is off, and will not turn on during the process.

Unscrew the unions at each end of the cell.

Visually inspect the cell for deposits. If it is cleaned on a regular basis, a garden hose with a spray nozzle will usually take care of the problems. Make sure you look through both ends while inspecting.

When working with any pool chemicals, in this case muriatic acid, use them carefully. The packaging will have safety information on it if needed.

For cells with substantial deposits that cannot be cleaned with a hose, It will be necessary to soak the cell in muriatic acid and water solution...4 parts water 1 part acid. Fill the solution in a bucket, or you can purchase a cell cleaning stand to do this. Do not submerge the cord in the solution.

It will start bubbling, and when the bubbling stops, it should be clean when the bubbling stops. For really bad deposits, I will allow it to soak for 10 min or so and then take it out and rinse it with plenty of water to try to break up and get rid of loose deposits, and re soak if necessary.

When you are done, rinse the cell well inside and out, and reinstall, making sure to check the orings on each side for wear and lubricate if needed.

If you let me know the controller, I can also tell you how to clear the Inspect cell message.