I have multiple Green Killing Machine 9w UV sterilizers in several of my tanks. Because I have a few of these, it gets expensive to replace the UV bulb every four months or so. If I put the sterilizers on a timer and run them only part of the day, this would mean that I might be able to go several years without having to replace the bulbs, but will a sterilizer be beneficial only running it part of the day or does it have to be on 24/7? If I can run only part of the day, how long should I run it for? Should I run it at night, in the daytime, or does it even matter when? Thanks!