Duckweed. Avoid this plant with every fiber of your body. It is so
prolific, a
tiny clump will cover the surface of your tank and block all the light
before
you know it. It's a weed, pure and simple.

Duckweed sometime will help you a lot. I had greed water for a long time. I
got few duckweed with some plants. I knowingly put them in my tank. Now I
have a group of them. They are really sucking extra nutrients.

--
Thank You

Dominic
http://www.dlink.org/aqua