The higher kelvin bulbs will help to bring out the color in your coral and fish. Especially the colors on the cool end of the spectrum. Some believe that is even promotes good color but i'm not sure i would support that.
In my opinion they give a nice tint of blue to the tank. Not all that noticeable until you put it next to some of the lower K
bulbs and then i think it looks much better.
The low K
bulbs are particularly good at plant growth which is good in freshwater but just translates to more algae in SW
. They are not recommended.
Many people will use a fairly white bulb as their main source (10-15000 K
) and then supplement with actinic bulbs to get that bit of blue and bring out the colors.