A system for treating water for use in aquatics or recreational facilities is disclosed. The system includes a media filter vessel, a pressure sensor, and a monochromatic light source. A method of treating water for use in aquatics or recreational facilities is also disclosed. The method includes fluidly connecting a media filter vessel to a source of water for use in aquatics or recreational facilities, illuminating a media inside the media filter vessel, observing a monochromatic light source display a first indicator and observing a monochromatic light source display a second indicator. A method of retrofitting a media filter vessel is also disclosed. The method includes installing a pressure sensor on the media filter vessel, installing a monochromatic light source and operably connecting the monochromatic light source to a manual control and to the pressure sensor.