Firstly, lets look at possible causes.
I use exclusivly Daltons and do not have green water issues, so maybe there are other factors.
You have not mentioned you lighting regime or intensity.
Have you tested the water for Phosphates??
How much are you feeding?
Where do you source your water?
There are many factors to keep in mind with algae, and unless you find the cause, you will more than likely be battling it again in the future.
WHile the Daphnia idea does work, It certainly will ot in a tank that houses fish. The fish will love you for it, but the Daphnia will not last more than ten minutes.
Here is a great link to an article about algae. Its causes and how to control it.
http://fishkeepers.co.nz/forums/viewtopic.php?f=50&t=287
HTH