I attended the IMAC over a year ago, and E. Borman gave a presentation. In the presentation he discussed the topic of the better growth on 10k ver 20k. He said that from his research that there is not a true 20 bulb on the market. He went on to say that at best the bulbs are 12-14k bulbs with high spikes in the blue spectrum. He also said that from his tests, sps did not grow any better than sps in a 20k tank. Just for thought. So, go for what looks good to you is the moral of the story.