Water Wisteria not growing well

I have some "water wisteria" in my tank. At the top of the plant it grows
nice green lush foliage. But in about a week, the tips of the leaves start
to curl under and turn brown and rot. New growth comes out of the top, old
growth slowly dies. My hornswort is growing like crazy. My lillies did well
in the tank. I add plant fertilizer stuff which is basically iron. Is this
just what the plant does, or is there some trick to making it grow healthy?