[coral reefer]

Let me ask you this before you decide to add another lighting arrangement!? Are you using carbon on your tank? Many times we, as glorified and dedicated reef addicts, think too much and overdo somethings when, in essence, we don't need to and we go into "overkill mode" IMO!
I think that many of us have too much dissolved organic and particulate matter, Gelbstoff, turbidity and and a film associated with the top of of tanks that basically refracts beneficial light from reaching our precious corals and Tridacna's below.
By removing some of these pollutants, excess nutrients and coloring agents affecting our tanks water quality and condition we will be able to ensure that more light will ultimately reach our livestock!
Cleaning your skimmer and other equipment for effective and efficient running and operation will aid this end result. Weekly water changes and not overfeeding should help as well.
Proper coral placement is also a key component to getting the best coloration, growth and health out of your corals and Clams.
Then their is the testing and possible supplemeting of benefical traces and vitamins, that are consumed rather quickly with carbon, skimming and livestock.
If after adhering to these steps, you still are not reaping the benefits for your corals, then you may want to try another light fixture!