Overview
A UV sterilizer passes tank water past an ultraviolet lamp that kills free-floating microorganisms, algae spores, bacteria, and some parasites, as they drift through. It is a useful tool for water clarity and disease control, but it is widely misunderstood, so it is worth knowing what it can and can’t do.
How It Works
Water flows through a chamber where a UV-C bulb irradiates it. Anything free-floating that passes close to the lamp long enough has its DNA scrambled and dies. The key phrase is free-floating: UV only affects what actually flows through the unit, at the right flow rate and with a bulb that isn’t old.
What It Does Well
It clears green water (algae blooms) fast, reduces free-floating bacteria, and can lower the water-column stage of parasites like ich and velvet, helping reduce outbreaks. It is also good general insurance in a fish-heavy system.
What It Doesn’t Do
It won’t cure an established ich or velvet infection, because parasites attached to fish or living in the substrate never pass through the UV. It doesn’t remove nitrate, phosphate, or dissolved organics. And it kills beneficial free-floating plankton and pods too, a minor downside in a reef.
Getting It Right
Flow rate matters. Too fast and water doesn’t dwell long enough to be sterilized; slower flow gives a stronger kill, so match the unit’s rated flow to its purpose, clarity versus sterilization. Replace the bulb roughly once a year even if it still lights, since UV output fades long before the bulb dies, and keep the quartz sleeve clean.
Frequently Asked Questions
What does a UV sterilizer do?
It kills free-floating microorganisms, algae spores, bacteria, and some parasites, as water flows past a UV-C lamp. It is used mainly for water clarity and as a supporting tool against disease.
Will a UV sterilizer cure ich?
No. It can reduce the free-floating stage of ich and velvet and lower the odds of an outbreak, but it can’t cure an established infection. Parasites on the fish or in the sand never pass through the unit, so quarantine and proper treatment are the real cures.
Does a UV sterilizer remove nitrate or phosphate?
No. UV only kills things that flow through it and does nothing for dissolved nutrients like nitrate and phosphate. Use skimming, water changes, GFO, or carbon dosing for those.
How often should I replace the UV bulb?
Roughly once a year. UV-C output fades well before the bulb stops lighting, so a bulb that still glows may have lost most of its germicidal power. Replace it annually and keep the quartz sleeve clean for full effect.