Stupid Lighting Question

It is true that algae likes light of the lower spectrum (more red). The higher the K value the more blue the light will be. You also start getting less coral growth with very high k values though. You need to decide what you want, more growth or more color. I guess 14 k is a good compromise.
I don't use halides but this would hold for all types of lighting. I can't give bulb recommendations though.

 

I'm very happy with my 20K bulbs.