This is a java fern http://www.java-plants.com/images/pl...2009%20010.jpg
Sword plants are quite nice, but they really need fertilization, root tabs really help. When you first plant them there is often leaf die off (I know from personal experience). For really good help with ammonia you want stem plants, moneywort, pennywort, anachris, cabomba, water sprite.
Many plants from larger stores like petsmart and petco are mislabled. Do you have a picture of the plant itself? You mentioned a LFS, so there are better odds it was at least labeled as the right kind of plant (a sword not java fern).