which light for algae scrubber

ok i set up an algae scrubber its a custom built tank 18" long x 10" wide x 16" tall
i want to get a good light that forces good chaeto growth for nutrient export
but im limited to a light that is 19" long so my choices are
a) 9" coralife power compact 2 - 9 watt 6700k bulbs 9 " x 5 1/4"
b) 18" coralife t-5 tube 1 - 15 watt 6500k bulb 18 1/4' x 4"
c) 12" coralife power compact 2 - 18 watt 50 / 50 bulbs 12" x 7"
d) 20" coralife power compact 1 - 28 watt 6700k bulb 20" x 5"
ok so heres my questions and concerns with each
a) not very long will the light cover the whole tank
b) never really heard good things about t-5 bulbs
c) they only make 50 / 50 bulbs for this fixture and i know
that 6500k or 6700k is best for my setup but does having a 6500k bulb really
make a noticeable difference over 1/2 actinic 03 / 1/2 10,000k bulbs when it comes
to growing macroalgae
d) slightly too long but the one i really want because of coverage , wattage and bulb
the bulb is only 14 1/2 " with endcap so i was wondering if i could shorten the
fixture im pretty handy when it comes to modifying things and since this is a pretty
basic fixture i dont think that their will be much wiring and stuff on the inside of the
housing on the end that is farthest from the endcap
and i really dont like any retrofit kits i prefer the complete housing
so any questions comments or advice would be appreciated
 
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