lighting, hmmm this is a huge topic, you should search it. there are SOOOO many opinions on here and different boards. this board will for sure tell you to get MH lights. and i didnt, i am going with 6- 160W VHO's on a 125 (dont have it yet, still on order)
some are going to tell you watts per gallon is not what you are really looking for, it is the intesity of light. soft corals do fine with less intesity but clams and such need more
you say you have 4w per gallon, but what kind of lights do you have? with the set up i mentioned, i will end up with i think 8-9w per gallon.
i am extremely frustrated over the lighting topic and i am sure a more experienced hobbiest will chime in and confuse the *&%$& out of you.
sorry if i was of no help, but hope you do a lighting search here