I just got a 45g high tank, it's about 24" high without any gravel. I intend
to use florrissant lighting. The tanks is 25" wide so after building a
canopy I shold be able to use 24" tubes. The tank in 18" deep. 25x18x24

What I am wondering is how many 20w tubes should I shoot for. The tank will
be a fairly low tech tank, no CO2 or substrate heating.

Any recommedations?