Ordinarily I don't recommend 20K bulbs as a single source of light because of their relatively low PAR (photosynthetic available radiaton) value. However, since its going over a 30 gal. I think it would be a relatively good choice. You are going to have so much light for that size tank that it would probably make up for the lower PAR value.
I've run Blueline 14K bulbs in the past. My opinion was that the color was good, but I didn't get the growth I was used to because of the lower PAR value. I went to a 10K when they 14K were due for replacement. I run actinic VHOs on that tank as well. I think the 14K would be a good choice too. A compromise between color and PAR.
Gary
Gary
125 SPS, 75 gal. LPS/softie reef, 9 gal. Nano