If you limit one or more available "ingredients" to make algae , well you wont have any . Correct me if I am wrong but I believe you need Phosphate ( lets face it everything needs phospates ) nitrate , Iron and potassium to form the basic building blocks of life . I am sure there are more but I believe these are the most important ones , I guess I should toss magnesium in there too . I don't use any GFO , or anything else just the occasional carbon or a polyfilter . I have a fuge running with cheato and a cheapo UFO grow light and my overflow has plenty of hair and turf algae in it to feed my yellow tang lol. SPS is starting to get better , LPS corals seem to thrive . But remember this tank is only 4 mos old