it will grow slower in cold water the reports you hear about it spreading like wildfire are normally in tropical tanks . ferts shouldnt be necessary, try replacing the tube in your lite as well dont know how old the 1 u got off me was , they lose most of thier useful light output after 8 months , a year(didnt know you would be having plants at the time) . a marine white would give a nice hue to ur tank i can tell you of a lighting wholesaler that will have these a lot cheaper than the lfs. other thing i have heard is that they like to have a bit of current around them so maybe point ur filter at them also. note: was in a drs surgery today next to eastgate mall the tank in there has the biggest jave fern ive ever seen the leaves are the size of my swords! but it has a big air pump with both outlets going into 1 tube and a silly ornament which lets up huge bubbles agitating the surface like a spa pool!