The Laguna PT523 is a replacement UV bulb for the following:
The PT523 Replacement 16w UV Bulb for Pond Sterilizer is a replacement UV lamp for the Power Clear UV Sterilizer/Clarifier 1000. This 16-watt pond clarifier lamp provides UV treatment within the inside chamber. This UV lamp sterilizes water to remove harmful microorganisms.
PT523 Replacement 16w UV Bulb for Pond Sterilizer specifications: