sterilizer will kill all living organisms in the water column IF it has enough time to work. You need to size the pump to the UV
used. If you use separate pumps for water circulation through your system and your UV
, and you properly size the pump to to give the correct water flow through the UV
, then the UV
will help keep algae, parasites, bacteria, etc in check.
If the UV
sterilizers has too much water flowing through it not much of anything will happen other than the waste of electricity used for turning it on.
Some people swear by them, some at them. I would suggest reading UV Sterilizers and Their Use in Aquaria
in the Articles section of this forum.