As an additional precaution, you could try raising your light fixture a few inches and slowly dropping it back down. However, you probably don't want to change too many things too quickly. The change from 20k to 14k is probably not the most drastic thing in the world, but still be careful!
I highly recommend those interested in researching MH bulbs/ballasts refer to Sanjay Joshi's work: http://www.manhattanreefs.com/lighting You can go through the little module under the 'Lamp & Ballast' tab and mess around with different lighting combinations. You'll probably be most interested in the "PPFD" value as this refers to a value similar to PAR (photosynthetically available radiation); higher values are better, lower values are not.
Daniel