It shines a pretty blue light into the water and it makes the parasites decided to be friends with the fish instead of infecting them….
JK, Water passes through the unit, and it gets absolutely blasted with UV radiation. This causes the reproductive parts of the parasite to be so badly damaged that they can no longer reproduce. IMO It is a very effective tool to reduce the risks of parasite breakouts. I personally would not run a tank without one after a bad experience without a UV one time.
The radiation is very strong, I had a small 18W unit, without thinking I took the light out of the sleeve to “check” it was working, ended up in the ER that night with radiation Burns to my eyes, no lasting effects but it freaked me out at the time and wanted to get it checked. -never look at a UV bulb**