I'm haven't used the Coralife 250W 20,000K, so I can't comment there.
However, Coralife sells three 175W bulbs:
5500K - Pretty much the same as a Venture or Hamilton 5500K. OK if you add enough supplemental blue.
6500K - A very nice bulb. Good output and PAR, but does require some supplemental blue to de-yellow the color.
10,000K - We often call this bulb the "Coraldeath 10K." It is VERY blue - too blue to provide much light at all. We use it over a deep ocean tank to simultate the light 10-20 feet underwater.
I had one about 4 years ago, sucker was BLUE, they used to have exploding problems back when they came out, how they came up with a 10kk rating is beyond me, maybe they suplimented with a 400w iwasaki for the test
I am not fond of Coralife halides. Their spectral outputs degrade quickly. Radium, Iwasaki and Ushio are the bulbs you should be looking at. Check out hellolights.com. Very good prices and selection.
Have had no problems with Ushio _and_ AB bulbs. I like the color of 250W AB 10K using HQI ballast. The 250W 10K W ushios are slightly yellow under HQI ballast if you can believe it.
You can get 250W 10K ABs from hello lights or ocean encounter for $78.
Avoid 20K bulbs in 175/250 W range, the PAR is just terrible. I believe they are OK in 400W bulbs for some reason.
thanks for the inputs i will have a look at a different configuration,right now i have 2 660 ice cap ballasts,2 250w ice cap ballasts, and 2 175w advanca ballasts. i want to put over a 150 6'L-18"w-26"t.
I´ve heard some bad comments about the coralife, and it is a too blue bulb, so that´s why I went with the USHIO.
I think you won´t regret buying the USHIO, also at premiumaquatics.com they have a good price and the customer service is awesome.