Most plants eat up Nitrates don't they? not pure ammonia as such.
Java Moss is quite slow growing, but once it's established it does really well in pretty much all lighting conditions. The stems attach themselves to whatever they are held on to, meaning it will grow up some decor you might have, if you wrap it on with cotton thread or something similar [using non-polythene covered cotton means the thread will rot, so you don't have to remove it once the Moss has a hold].
Most fish seem to leave it alone as well [apparently it has a bitter taste], although if you attach it with cotton, make sure all the thread is secure, as scavaging fish might undo your hard work, sending the moss in whatever direction your filter outlets facing.
Overall it's a gorgeous plant to have growing over rocks and wood etc. You can even make a 'moss wall' using thin plastic mesh with the plant inbetween. Lovely stuff.
A great site for most aquatic plant info...
Java Moss @ www.tropica.com