"The GreenFree UV 2 provides permanent control of algae. It removes heavy algae blooms usually within 5 days and keeps the pond algae free. The TetraPond GreenFree clears water while reducing pond maintenance. It is compact, durable, easy to install and energy efficient and delivers full power from the ultraviolet bulb (bulb included). The GreenFree has a transparent inlet/outlet that allows easy viewing of flowrate and bulb function. Good for ponds up to 4,400 gallons of water. "