These are going to grow up and be huge. For now, what you are getting is a junior sprout over 6 inches long. These plants take a second to get established and hate being moved.
I recommend slightly harder water, but they can handle most anything.
You might want to pick up some Mystery snails as they seem to do a nice job cleaning these plants off as well.
These are priced to move as I typically sell small ones for $19.95. This deal wont last.