UV's sterilize the water pretty well if the bulb is still good and it is an appropriate size. Sometimes they can be bad if they are over spec or on too long and the will take out too many beneficial organisms as well as the bad ones.
UV filters are good if used properly. You just have to install them in the right place, have the correct amount of water flow through them and make sure you change the bulbs every 9-12 months. There is no need to have a timer on it.