I agree. A friend of mine had a 2.5 foot mangrove for over 5 years that he just got rid of it. He sold it online, and the guy had to drive up to pick it up because it was attached so well to the 20 gallon tank.
I would look towards getting chaeto, caulerpa, halimedia, shave brushes, things of that nature. All of that stuff will grow very well, and but are managable.