Most BP manufacturers recommend not using uv along with BP's. I would take the uv off line during the start up of the BP reactor until you see some effect from using the BP's. Then, if you decide you want to try it, redeploy the uv, and see what kind of affect it has. It shouldn't have any affect on the bacteria that remain in the BP reactor, but can/will destroy much of the bacteria that will go through it, overall limiting the uptake of N's and P's in your system.