PlanetCatfish.com

I would like to know how UV serilizers affect the benificial bacteria in the tank system?

Are they best ahead of a filter, after, or on there own circulator?

On this topic, does anyone know if the home sterilizers have a check-valve, to stop the migration of bacteria into the post strilized pipes, when the water flow is stopped between uses?

UV sterilizers do not effect the beneficial bacteria. They are attached safely out of harms way on the filter media.
A check or foot valve could no harm but it is really nothing to be concerned with.

The UV is supposed to be connected on the output flow of the filter. Make sure you buy the correct UV to match your filter flow for the best dwell time (length of time the water makes contact with the UV light). For example, do not buy a 9 watt UV filter, which you plan to connect on a Eheim Pro II 2128.