UGH! I'm really starting to hate the color green!

If you have something like high phosphates in your local water then your water changes are feeding the algae...

I've used UV lights for 5 years or so... I love them... The will eliminate all free floating algae and will reduce surface algae... As a bonus they kill parasites and make the water truly crystal clear. Sure they cost a bit, but to me their benefits are worth it for a display tank.

I have Turbo Twist lights and they work great... I like the way they hang on the side of a tank which is great for a unit used to move between tanks...

My preferred brand is Danner as they are built very tough and meant to last. They're housing is also UV resistant.

I've never used Aqua Ultraviolet sterilizers but to be honest... I've never gotten a bad review from a UV light that was properly used... As long as it doesn't leak and the bulb works... the light pretty much does what it's supposed to do...

A UV sterilizer is really only necessary for green water, if you have algae sticking on the glass or covering your substrate a sterilizer will only be marginally useful. The answer to many algae questions in a non-planted tank is to reduce the amount of light. Turning off all the lights and covering the glass with something like a black trash bag to block all light for 3-5 days will pretty much kill most algae (except green water, UV sterilizers are known to be effective on green water.) After turning on the lights you'll want to control the time and intensity of the light. Your fish don't need the light to see, ambient light through a window will be enough for them to see food and keep from running into decorations, except in planted tanks I only turn on the lights when I expect to glance at the aquarium. Usually after I get home from work I'll go through the house and turn on the lights (on my planted tanks that have timers set to come on just before I get home) and feed the fish then switch the lights off before I go to bed. I have my lights on for 5-6 hours in the afternoon and evening and that's it. I've had very few problems with algae this way.

You should test for ammonia before and after a water change, ammonia is known to trigger algae growth because it can actually use the nitrogen in ammonia faster than it can use nitrogen in nitrate. If you are getting an ammonia spike that could be part of your problem.

I know it sounds a little backward but if your gettting blooms after a water change maybe you need to stop doing so many water changes. The nutrients in your tap water are what is feeding the algae, if you deprive the algae of nutirents it will die. Don't worry so much about your water quality, the algae will eat nitrate and other wastes so you can extend the time between water changes a little more than if you didn't have the algae.

I think the first thing to do is identify the cause.

phosphates in the water are quite often the culprit. so the use of a phosphate remover should sort it.

a UV steriliser/clarifier treats the problem(of green water, not algae on tank/décor), but doesn't solve it. so you are adding another bit of equipment that needs to be maintained and running costs. and the moment you remove it it comes back.(clarifier's are usually used on ponds and are therefore cheaper per watt, however, three is a larger gap between bulb and wall, so they only kill some of the algae spores, and the odd bacteria/virus. steriliser's have a much narrower gap, and will therefore kill all organisms in there.)

as others have suggested, get a report form the water company. this should give an indication whether its the tap water causing it.

another thing to note, if you are feeding frozen foods, rinse off the thawed juice first, as this is extremely high in phosphates.