Curling Anacharis?

[anvil63]

I've had plants for years, but I got some anacharis for the first time a few weeks ago. It is growing like wildfire, but everyday by the time lights shut off the top of each plant has curled over so that every plant resembles a cane. By the next morning the plants are straight and once again slowly begin to curl over.

Lights are on for two five hour periods with a 2 hr siesta
right now have 8x30w flourescent tubes over tank (150g tank)

Carl