I feel tat so long the coral can't get enough light, no matter how long u on the light also not much effect. Or maybe u need to on very very long, not just few hrs more .
I think like wat Sherman said, most effective n cost saving is lower the light set.
But u lose the spread, so u need buy another light set...
But I think sps not enough par will lose coloration, n having longer photoperiod not going to help.