Having green water is never cool... I had that happen on my first hydro grow. I fixed the problem by pulling my plants out, and bleaching my entire setup. You can do this by mixing you a five gallon bucket of bleach-water, submersing your pump in it, and pumping the bleach-water through your entire setup. (DONT FORGET TO TAKE THE PLANTS OUT!!!) After your done, Flush the whole thing with a five gallon bucket of normal water. Replace your plants and go from there.
That's the only SURE-FIX I know of.
Just another little note... You should sanitize your reservoir at least once a week.
Good luck!