What length? I have a brand new 36" 75/25 UVL aquablue. How many bulbs do you need? I would say that for a clean, crisp white/blue, you should go for half ATI blue plus and half ATI aquablue specials. The aquablue specials are really white and the blue plus are really blue. If you have a six bulb, I would go with three blue plus, two aqua blue specials and one of the UVL bulbs like I have, the aquablue 75/25. Its a bit pink, but puts off tons of light and makes the reds and oranges pop with some actinic glow. Lay off the UVL bulb if you only have a 4 bulb fixture like mine. I bought it but replaced it with another blue. Tank looks ten times better since you were here.