i was under the impression that although new plants often melt or take time to acclimate to a new fish tank, they eventually start flourishing. However, the impressive growth you see in the beginning isn't due to the conditions in the new tank but built up reserves from where they were grown. Therefore, the hard part isn't getting plants to survive but to maintain growth. I'm guessing your plants grew initially well but eventually ran out of nutrients and died. I'm probably wrong though...