I have a background in marine biology, and I can assure you that the spectrum needs of underwater (marine) life is quite different than those on the surface. Specifically, the red spectrum of the sunlight is stripped as it travels through the ocean water to where the corals live, so most corals use the blue spectrum. This is why synthetic lights used in the ornamental marine business are typically 10k, 14k, 20k (although I have never seen a 30k bulb before). They are also used for aesthetic value as coral contain zooxanthellae that live within the corals' tissue and reacts to the blue/purple spectrum and reflect an almost glow like appearance. As for the MJ - you want to use a bulb that will allow maximum spectrum absorption, which happens to be in the red/yellow side of the spectrum. (4-7k) for veg, and typically more red for flowering (~3k). You could use the higher K bulbs, but your plants will suffer as they will not get enough light energy that they can actually absorb - and you waste all that electricity by producing a light that is not used.
