About the 18w Single-Ended UVC Bulb - BOGOF Manufacturer: UVC Bulbs ADD ONE 18W BULB TO YOUR BASKET AND RECEIVE TWO!!! MORE EFFICIENT, BETTER FLOW BETWEEN TUBESPopular replacement bulb for pond UVC units and filters which fits the following filtration systems: FiltersBlagdon Midipond 20000Evolution Aqua EazyPod Automatic CompleteEvolution Aqua Eazypod Complete GreenEvolution Aqua Eazypod Grey CompleteHozelock Bioforce Revolution 6000 Laguna Pressure Flo 10000**Oase Bitron 18Oase Filtoclear 12000PondXpert EasyFilter 20000PondXpert Filtobox 12000PondXpert SpinClean 20000 (pre-2019 version)Velda Clear Control 50 UVCsBlagdon ProPondXpert Greenstop 15000 ** If your Laguna filter was manufactured pre-2015 you need an official Laguna 20w bulb, however a regular 18w bulb is sufficient with any models made 2015 onwards.