A UV sterilizer can reduce free-floating pests in a reef tank. It works best when you size it correctly and tune the flow. This guide shows practical setup steps and common mistakes.
What a UV sterilizer does in a reef tank
A UV sterilizer exposes water to ultraviolet light inside a chamber. It damages DNA in algae, bacteria, and parasites. Only organisms that pass through the unit are affected.
UV helps most with green water, bacterial haze, and waterborne stages of ich. It does not cure parasites already on fish. It also will not fix poor husbandry or unstable parameters.
Think of UV as a support tool. It complements quarantine, nutrition, and stable salinity. If you skip quarantine, UV may only reduce outbreaks, not prevent them.
UV can slightly reduce plankton in the water column. This can affect filter feeders in very small systems. Many reef tanks see no noticeable downside when flow is set well.
- Best use cases: green water, bacterial blooms, parasite management
- Not a use case: replacing quarantine or treating infected fish
- Expectation: clearer water and lower disease pressure over time
Sizing, flow rate, and placement for real results
Match wattage and flow to your goal. For algae and clarity, higher flow is fine. For parasite management, slower flow and longer contact time matter.
Use these practical targets for many reef tanks. Aim for 1 to 2 times display volume per hour for parasite control. Aim for 3 to 5 times per hour for water clarity. Example: a 75-gallon tank often runs 75 to 150 GPH for parasites.
Plumb the UV after mechanical filtration for best performance. A clean sock or roller reduces debris in the chamber. Debris blocks UV and lowers effective dose.
Placement options depend on your sump and pumps. A dedicated feed pump gives stable flow. A manifold off the return works if you can measure GPH. For planning sump layout, see reef tank sump setup.
- Use a valve and flow meter if possible
- Keep tubing runs short to reduce flow loss
- Mount the unit where you can service it easily
Maintenance, troubleshooting, and common mistakes
UV performance drops with dirty sleeves and old bulbs. Clean the quartz sleeve every 4 to 8 weeks. Use vinegar and a soft cloth. Rinse well before reassembly.
Replace bulbs on schedule even if they still light. Many bulbs lose output after 9 to 12 months of run time. Mark the install date on the housing with tape.
If water stays cloudy, check three things first. Verify flow rate matches your goal. Confirm the sleeve is clear. Confirm the unit is fed with filtered water. Also test nutrients and filtration. For bloom control steps, see bacterial bloom in reef tank.
A common mistake is running UV too fast and expecting parasite control. Another mistake is skipping quarantine and adding stressed fish. Use saltwater fish quarantine for new arrivals. UV then becomes a strong safety net.
- Microbubbles: check pump intake and tighten unions
- Heat rise: increase sump ventilation or run at night
- Leaking: replace O-rings and avoid overtightening
Optional: A simple setup checklist for a 75–120 gallon reef
Start with a UV sized one step above your tank volume. Many hobbyists choose 25 to 40 watts for this range. Use a dedicated pump that can deliver 100 to 300 GPH after head loss.
Set initial flow for your main goal. Run 120 GPH for parasite management on a 90-gallon system. Run 300 GPH if you only want clearer water. Recheck flow after cleaning the sock or roller.
Run UV 24/7 for consistent results. Turn it off during certain coral foods if you prefer. Restart it after 30 to 60 minutes. Keep salinity stable at 1.025 to 1.026 and temperature at 77 to 79°F.
Log changes for two weeks. Note clarity, fish behavior, and skimmer output. Adjust flow in small steps. This prevents chasing problems and overcorrecting.
Sources: TMC UV sizing guidance (manufacturer documentation); Pentair Aquatic Eco-Systems UV application notes; Noga, “Fish Disease: Diagnosis and Treatment.”
A UV sterilizer can be a smart upgrade for reef stability. Size it for your goal and control the flow. Maintain the sleeve and bulb on schedule for dependable results.
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