fluorescent bulbs

I have a 20 gallons tank. The lighting system is composed by two 15W
fluorescent bulbs. When I bought them, the vendor assured me that
they had a different spectrum. All I can see on them is the name:
AQUA-GLO and AQUA-STAR respectively (I think they are made in German).
I would like to know the difference between the two bulbs (and some
other questions):

 -- At what frequency does every bulb have its maximum of light intensity?
    (maybe it is written somewhere? The vendors are not very expert
     on this argument)

 -- What frequency is more required by plants?
    (I heard that they use primarily ultraviolet and infrared)
 -- And what by fishes? (a friend told me that fishes do not care at all
    about light)

 -- How many bulbs is it recommended to have?

Every advice will be welcome.

  Dep. of Phisics, University "La Sapienza", Rome.
  E-mail: vari at sunset_roma1.infn.it