ok, here is a bit of science now, your best bet is to have some red and some blue color led's, at the 440nm and 670nm spectrums of light. Those two color coincide with the peak absorption of chlorophyll I and II, you will see more growth and better survival of your cheato there than with just white light.
The better absorption, the more energy used, the more phosphates and nitrates being used by your macro algea.