kooky has a good point about uv lights. if they say they last 12 months, you probably should change them out at 10. they gradually deteriorate so the output might be 40 percent by then. the other issue is whether or not you really need a uv light on that pond. is it shaded by landscaping? plus, English skies are not especially blue most of the time, so how much do you really need? i've got a 4000 gallon pond, but i only use a 25 watt uv because of the amount of shade, and it works just fine. i don't know if you can do it, but the quartz sleeve will become coated with junk and attenuate the uv rays. can you wipe it off? mine came with a wiper that seems to help.
the other thing is to make sure you can still get a replacement bulb for your uv. sometimes they stop making a certain model. and when you decide to change the bulb, read the uv instructions. you can find them online with the manufacturer if you don't have them. the most common problem with a uv is breaking the quartz sleeve when you change the bulb.