Ok so you've already got the two 175 watt Metal Halides with bulbs that have a color temperature of 10,000K. You want to replace these with bulbs of the same wattage (175w) but a higher color temperature (40,000K)?
If that's what you're asking, I definitely do not think that is a good idea. While plants do rely heavily on blue light for plant growth, they also need strong output in the red are of the spectrum. I'd actually look at bulbs in the 5000K - 6700K region, but if yours are still working, I wouldnt' change a thing. Next bulb change you can try a lower color temperature.
- Sam P -
plantedtanker in limbo - all tanks currently in storage