Very few algae use the blue spectrum for photosynthesis....That's why the deeper you go in the ocean the less algae you find...I have found that old bulbs as they fall off in proper spectrum have the habitit in helping some algae grow, but that is just my opinion or it seems like it to me.....When did you change to that light combo? What was it before? The way you typed it, it sounds like you had a differant combo on the tank before this.