low PH bad bulbs and tap water is all common reasons for it
Raising the PH and magnesium adding a clean up crew or algea grazing fish PENDING TANK SIZE foxface or tangs and getting new bulbs all ways to help keep under control
Are you buying his setup? Or are you just buying the rocks? If you are just buying the rocks I would suggest a few buckets or bins (that have NEVER had any chemicals in them) half way filled with prepared ro/di water with salt and proper temp and a couple of (new) stiff brushes. And scrub away all of the algea and don't forget to rinse them well. This would be the quickess way to remove it. Then add some hair algea eating inverts, a algea blenny(but they are not always quaranteed to eat the algea.) Best wishes...