If you like blue use kz super blue. Much nicer than any ati blue bulb. Bluer and the same par. In my four bulb combo I run 2 super blue, dusk and then a kz fiji purple. I picked up an aqua science duo that is wonderful. More of a 15 k bulb. With this combo the tank is bluish white and very crisp. I believe the super blues are about 17k if I am not mistaken but have a par of about 330. Fiji purple also has a par in that range.