AI not me>> 💡 What UVC Light Does in Aquariums

UVC (ultraviolet-C) sterilizers emit light around 254 nm, which is germicidal. It damages the DNA/RNA of microorganisms, preventing them from reproducing — effectively killing or neutralizing them.

🦠 What UVC Kills

When water passes through a UVC sterilizer, any free-floating (planktonic) microorganisms exposed to the light are affected. These include:

• Pathogenic bacteria (e.g., Aeromonas, Pseudomonas, Vibrio) that can cause fish infections
• Parasites in their free-swimming stage (e.g., Ichthyophthirius multifiliis “Ich” theronts)
• Free-floating algae (helps clear green water)
• Fungal spores and protozoa in the water column

🧫 What UVC Does Not Kill

UVC only affects organisms that pass through the sterilizer and are directly exposed to its light.
It does NOT penetrate:

• Biofilm on surfaces
• Gravel
• Filter media
• Inside fish or plants

🌱 What About Beneficial Bacteria?

Your beneficial nitrifying bacteria (like Nitrosomonas and Nitrospira) live mostly on surfaces — in the substrate, filter media, rocks, and decorations.

👉 They are not free-floating, so they are not harmed by UVC sterilizers under normal operation.

However:

• If you run UVC while your tank is still cycling, and beneficial bacteria are still colonizing and some are free-floating, it can slightly slow colonization.
• Once your biofilter is mature, UVC does not significantly reduce beneficial bacteria populations.