How often should I replace UV sterilizer bulbs on a reef tank?
Quick Answer
Most reef keepers should replace UV sterilizer bulbs every 9-12 months of actual run time, then confirm output with clean quartz sleeves and stable flow rates.
Replace UV sterilizer bulbs about every 9-12 months if the unit runs continuously. Even when a bulb still lights up, UV-C output drops over time, so old bulbs can look fine but disinfect poorly.
A good maintenance routine is to clean the quartz sleeve every 4-8 weeks, verify pump flow matches the UV unit target, and replace the bulb on a calendar reminder instead of waiting for visible problems.
If your reef has a heavy fish load or frequent disease pressure, stay closer to the 9-month mark. Lower-risk systems can often run to 12 months if flow and sleeve cleanliness are controlled.
After replacement, recheck temperature and flow for 24 hours and watch fish behavior. Consistent UV maintenance supports clearer water and helps reduce free-floating pathogens without replacing quarantine or stable husbandry.
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