Years ago (1995), I had a green water problem as well. I asked the people at the LFS what to do, and they sold me a Vortex Diatom filter.
http://www.diatomfilter.com/index.htm http://www.diatomfilters.com/index1....d=38747.666308
It worked like a charm, and I have used a diatom filter for maintenance ever since (although I don't remember having had green water since then). Of course, this method involves buying a piece of equipment, and you've already mentioned not wanting the expense of an UV sterilizer. I'm not sure I would use one of those on a planted tank anyway. I've read something about how they aren't good for your fertilization (possibly breaking down the chelates or ferts, maybe?), although I don't remember the specifics. However, I am quickly figuring out that here on APC you're liable to have all sorts of opinions, so someone will probably chime in and say that you should use one and that they've been using theirs for x years with no problems.
The point is, a diatom filter will filter out really small particles, including planktonic green algae. Supposedly they will even filter out the parasites that cause ick. I use mine about once a month and don't have any issues.
However, I will mention that I have had problems where the electric motor shaft seal will leak water. I used my original one for years, then it started leaking, and I tried to install a reseal kit without any luck. I then bought a whole new unit, and eventually it leaked, too. This time though, I removed the electric motor, modified the pump housing, and installed an external pump. So far it is working great. My Father-in-law has got to be about one of the best people in the world at finding good deals. He has actually bought several from places like thrift stores, auctions, flea markets, yard sales, etc. You might could find one really cheaply like that and I'd be happy to show you how I replaced the pump on mine (that is if the one on the unit is bad or leaking). Then all you'd have to buy is the diatomaceous earth, and maybe a replacment filter bag. Just a thought.
I also noticed that the second web page that I listed for you mentioned that pretty much everything has been discontinued due to manufacturer issues. I have no idea what that means. This might mean you won't be able to get one. When my first one started leaking, I tried to see if any other manufacturer offered diatom filters, but didn't have any luck. I also wouldn't recommend getting the recharge valve. I've had two different versions, and they both were junk.
As I mentioned before, there are lots of opinions out there, so someone will also probably say you shouldn't use diatom filters as well.
Andy