Originally Posted by MattsBettas
It won't eliminate all of the bad bacteria, and even if it did the good bacteria would die to. I don't use uv sterilizers because:
1) They are never 100% effective- and that one percent of the bacteria that survived will just repopulate.
2) They are not cheap.
3) They are completely unnecessary in my opinion.
Now for the other side of the story...
1. They are very effective at removing not only bacteria, but parasitic, fungal, and viral pathogens. Repopulation would only happen if you turned the sterilizer off. It's supposed to remain on at all times, just like a pump.
2. Some are cheapER. Overall though, they are geared towards larger aquariums with larger populations of fish.
3. While not necessary, per se, they can be very useful in reducing the risk of fish getting sick. Especially in tanks with large populations, or tanks with a transient population.
P.S. The good bacteria are not affected with UV sterilizers since the the vast majority of good bacteria are attached to substrate and the aquarium filter. UV sterilizers only treat the water itself. It's a glorified water pump essentially.
I'm not promoting these things by any means. I'm just trying to make the argument fair and balanced.