UV Sterlizer

I have a 75G fish only sal****er tank that if I had to guess has about
30 pound of live rock. Right now its on a really light bio-load with
two Marineland filters: Emperor 400 and a canister 350. What size and
brand/type of UV sterlizer should I get? I was thinking of a unit to
hang off the back of the tank with its own pump or run the return half
of the water from the 350 that goes out the nozzle and not the
bio-wheels through it. I'm thinking that 25 watts is a fair size to use
with a flow rate in the high 200s to mid 300s GPH...

Thanks,
Jeff