Evolution Aquas replacement quartz tubes 15w / 25w / 30w / 55w are designed specifically to replace the existing quartz sleeves in the Evolution Aqua EVO clarifier range. There are two quartz available - one for the EVO15 / EVO25, and another for the EVO30 / EVO55. These quartz sleeves help protect the bulb unit from air and water flow, breakage, leakage, temperature fluctuations, and environmental hazards. They should be replaced once a year as algae and dirt can cloud the tube making the UV bulb less effective. It's also advisable to replace the rubber O-rings (sold separately) for your quartz yearly as these can go brittle and crack. Specifications For Use With: Evolution Aqua clarifier EVO15 / EVO25 / EVO30 / EVO55 models EVO 15/25 model: Length: 41.5cm EVO 30/55 model: Length: 87cm Internal Diameter for both: 2.6cm