Using a UV Sterilizer for Disease and Parasite Control
A UV sterilizer kills free-floating pathogens and free-swimming parasite stages in the water column, but it does not cure an infected fish. Learn what it can and cannot do, and how to run it.
A UV sterilizer is a tube containing a germicidal ultraviolet lamp that water flows past. It is a genuinely useful disease-control tool, but it is also one of the most misunderstood pieces of aquarium equipment. Knowing exactly what it kills, and what it cannot touch, is the difference between a helpful aid and false confidence.
How it works
The lamp emits short-wavelength UV-C light, roughly in the 200 to 280 nanometre band, with common mercury lamps emitting at about 254 nm. This wavelength is strongly absorbed by the nucleic acids of microorganisms and damages their DNA, so that as water passes the lamp, free-floating bacteria, viruses, protozoa, algae cells and spores are inactivated and can no longer reproduce. The effect depends on UV dose, the product of light intensity and exposure time.
What it can do
- Kill free-floating microorganisms passing through the chamber: water-borne bacteria, free algae cells (the cause of green water), and fungal or algal spores.
- Inactivate the free-swimming stages of some parasites in the water column, such as the tomites of ich, reducing reinfection pressure.
- Lower the spread of water-borne pathogens between fish and across a shared system.
Running it correctly
For disease support, dose matters: a slower flow rate through the unit gives each volume of water longer exposure and a higher kill rate, so disease-control flow is slower than clarifier flow. Place the unit after mechanical and biological filtration so the water reaching it is clear, because suspended particles shield microbes from the light and let them pass unharmed. Run it continuously for ongoing protection.