In hard water areas a build-up of minerals may occur where water drops have not been removed. To remove these easily diluted white vinegar should be used to wipe down the glass.
In extreme hard water areas we recommended using undiluted vinegar every week.

Caution: Avoid the use of harsh or abrasive cleaning products which may damage the treatment and void the warranty - includes water spot removers, toothpaste, polishes, rough, or gritty substances, and products such as Ajax or Jif.

With correct maintenance these products are never required.

If the recommended maintenance has not been followed for some time, just as it took time for the build up to occur, it will take time to remove the debris from the protected glass surface. This can most commonly be achieved using undiluted white vinegar dampened on a Magic Eraser. Depending on the severity of the build-up this may take multiple attempts, but once the glass is clean again it will perform like new with the EnduroShield protection still intact.