[kien]

A touch of blue in a coral tank looks great but keep in mind that if you plan on continuing to use your supplemental actinics, those put out a lot of blue also. If you plug in 20k halides you may find that there will be too much blue!

Generally speaking people who run 20k halides don't need or want to supplement with anything else. So if you go this route, you could in theory stop using the actinics. Generally speaking again (and in my opionion) these types of combo fixtures are meant to utilize the actinics to add that touch of blue to complemt less bluer bulbs like 10k or 14k halides. I've never run 20ks but I would guess that a bluer 14k halide with actinics would look similar to just running 20ks alone. Now, I say bluer 14Ks because some 14ks are much more white than blue.

Where these combo lights excell is there ability to compromise between great growing lights (such as 10Ks) and the nice look of a blue light.

In the end it all boils down to personal taste though. Just because someone likes to blast their tank with blue light doesn't mean you will. Just because one or two people don't mind the yellower glow favouring growth doesn't mean you will or will not :-)