Frill plant, or Myriophyllum, needs more light than 30w IMO. Smaller tanks need more light. Its probably a CO2 issue as well as a nutrient issue. I'd start with atleast 40w over the tank, maybe more, add CO2 and then dose some macro nutrients (Potassium, Nitrates) along with the micros (Flourish).....then let us know how the plant is doing.
