I have always thought of water sprite as a warm water species. Growth of my plants seem to be directly proportional to temperature and N concentration. But like you, I have noticed that stressed plants produce more plantlets than ones in constant growing conditions. I would expect the young plants to grow well for you.
Eheim Pimp #181
29g High-tech jungle
5.5g Low-tech jungle
2.5g x 2 Low-tech shrimp and moss