lotus plant size?

Hi all I have a "Nymphaea lotus var. rubra" it has red leaves with dark red
markings. The leaves are growing 8" to 10" across, Why?
Any pix I see on the web, show nice clusters with perhaps 20 or so 2" leaves,
as opposed to my lotus that sends out these giant leaves straight to the
surface, but only 5 or 6 at one time before some begin to desicate and are than
replaced by the plant. My lighting is 2 watts per gal. (gro lux) in a 18" deep
tank I also use D.I.Y. co2 about 25ppm. Can anyone give me some idea as to how
to reduce the leave size and increase the total number of leaves. These giant
leaves are shading out my other plants and sometimes need to be removed,
something I hate doing to healthy plant matter. I use fert.tabs for root
feeding and that's about all Any and all advice & ideas are appreciated and
welcome As always T.I.A. and regards Art