Just a little bit of info for you guys that you might find useful. I have always used ATI bulbs as well. GREAT bulbs. However, my LFS has recently started carrying the new line of Giesemann bulbs. It's a completely different line, as Giesemann redid them in fall of last year. I have a 4 bulb fixture and this is what I run
Front
giesemann aquablue azure
ATI Blue +
giesemann aquablue coral
ATI Blue +
The look to ME is roughly 16-18k
My observations:
The Giesemann Aquablue Azure is unmatched by any bulb currently made by ATI. It's a white bulb with a turquoise tint to it (although very very slight) it does not make my tank look turquoise. It's not overpowering, and gives my tank a very nice look when combined with the other bulbs. The giesemann aquablue coral is very very similar to the ATI Coral + bulb. I really can't see a difference between the two.
I have tried the ATI Aquablue Special before and hated it because it washed out my colors. The Giesemann Aquablue Azure does not have that same effect, and as I stated, the Giesemann Aquablue Coral is essentially an ATI Coral+ counterpart.