175w halides are not that strong and should cause no problems. Even 250w are easy to acclimate corals grown under low lighting. I would take it a little slower with the 400w halides though and bring up the exposure time over a week or two. 400w halides will provide the best light and intensity. I have found 250w DE/sunlight supply will keep your color, but 175 and 150s tend to turn everything green or brown. I believe they turn green and brown in an effort to try to produce enough food for themselves, which would indicate a little more light would greatly improve overall health.