I would likely start it near the bottom and work it up. I do that for most corals, unless I know where it came from. Ask the person you got it from where they had it in the tank and under what kind of lights. That is always a good starting point. With a 58 gallon (I'm assuming somewhere between 17-22" tall) with a 150 HQI, you can probably start around the top of the lower 1/3 with no issues. Mine are in the sand and are turning brown. That is under 250W DE AB 10K's and VHO's, though. They've never had color under these lights...