I've read that it removes a lot of ammonia,nitrate, and nitrite.
The only thing that would be a problem is if it blocks out all the light
from my plants. If I kept it in my aquarium, could I easily remove
all of it, or is it like duckweed....
You shouldn't have any ammonia or nitrites in a properly cycled tank. It does a decent job of removing nitrates though. It's easily removable since it grows much larger than duckweed. It doesn't like surface agitation though.
Yup you can just take it out every week and toss as much of it as you want (: All you need is one plant and it'll grow back again and cover the surface in no time. It's great at sucking up nutrients and shrimp LOVE hanging out on it and cleaning the roots.
You shouldn't have any ammonia or nitrites in a properly cycled tank.
Ammonia will always be in the tank if you're feeding your fish, but it is just consumed so quickly that tests will read zero. Plants will consume ammonia, and if I recall correctly it's even preferred over nitrate.