UV bulbs need to be replaced after 12 months of operation in order to maintain crystal clear water in your pond.  If you shut down your pond furing the winter, you may only need to replace your bulb once every 1.5 to 2 years.  If it is time to replace your bulb, you will notice that your pond water will start to turn brown or green.  Replacing your UV light bulb is simple, unplug the unit, remove the old bulb and then replace it with a new one.  Be careful not to touch the glass on the bulb, fingerprints will create hot spots and will damage the bulb   17  in long