A little robot that scours the display panels and gradually "sterilizes" them by slowly walking a small volume, highly insulated cup with a heating element inside of the cleaning chamber over the panels a little bit at a time. The isolated water inside of the cup would be heated to around 180 degrees, which is far enough below the softening point of acrylic and certainly would kill pretty much anything growing on them. A small amount of fresh tank water would have to be periodically drawn into the cleaning chamber and used to flush out any detached buildup and sand grains to prevent scratching. With such a small volume of heated water being continually circulated, I doubt it would cause a noticeable elevation in over all tank temperature.