These replacement UV lamps are ultraviolet bulbs for Pondmaster® Clearguard™ pressure filters. UV light helps control green water and enhances the cleaning action of any Clearguard™ pond filter (maximum of 2 UV lights can be placed in any Clearguard™ unit). SKU UPC Code Description Compatible with 15615 025033156159 9W UV Bulb (4 Pin, Square) Clearguard 2700 (#05610) 15625 — 18W UV Bulb (OLD Style — 4 Pin, Square)DISCONTINUED — 15628 025033156289 18W UV Bulb(NEW Style — 4 Pin, Straight) Clearguard 5500 (#05620)Clearguard 8000 (#05630)Clearguard 16000 (#05640) 15851 025033158511 36W UV Bulb (4 Pin, Straight) Clearguard 8000 (#05630)Clearguard 16000 (#05640) NOTE: The manufacturer has discontinued the old-style Pondmaster 18W UV Bulb (4 pins in a rectangular arrangement). If your UV clarifier uses this bulb, you will need to change out the hardware so that you can use the new-style bulb from now on.