growing coraline algae

I can't seem to grow or maintain new Coraline algae. I have a 75 gallon Fowler tank. 20gal sump . I have 35 pounds of gulf live rock. That had beautiful purples and oranges and reds Coraline algae. But now it is looking kind of dull and brownish. I just added 40 pounds of dry rock that I want to...