you can keep sps at the top with even so so reflectors. the key phrase is "at the top". at the top on a 120g is no different than at the top of a 30g. there is the camp that believes 150w Mh arent appropriate for a full blown sps tank which I sort of agree with (too many placement stipulations, dependence on water clarity and slow growth) BUT that being said I have mostly sps all 6-11" from the top using 150w x2 sunpod and 20k bulbs and no issues. colors are as they should be, growth obviously could be better but they do grow. For a MIXED tank with SOME sps at the top 150w work just fine. I have monti cap frags on the bottom of the same (17" tank) and for kicks put 2 frags from the same cap in my 14g biocube with stock pc and they have retained their color and thrive/grown in the several months they've been in there. all sps arent created equal, there are enough moderate light requiring sps and even acro's where no one would even expect they are doing so well because you chose carefully and not expect the weak lighting. for example tri-color validas, ORA's roscoes blue, green mili's, most monti's ect ect ect will do just fine under 150w where a acro hyacinthus or humilis would be served better under the best 250w or 400w combo there is to be had.