NO/HO are available in a myriad of length's over 24"... below 24" will generally be T8's, think there may be some shorter T12's around.
For us, a 96w quad over a 10g tank worked very well, obviously closer to 4X the light of the 28w deal... with a little patience you can get the 96w quad in a retro kit (including all the tube, wiring and workhorse 5 ballast) for around $20-30 on eBay... even with a cobbled together reflector the light is great. That's my nickel worth.