Here is the typical sequence of algae on a new screen: First is a light brown coating, like a slime. After a week of that, you clean it lightly, and the next week you get a darker brown. After you clean that, you'll either get very dark brown/black stuff which stays very hard and thin, or you'll start getting some green hair. If it's the dark stuff, clean it right way (don't wait a week). After a few cleanings of this dark stuff, it too will start turning green. After a month or two, most of the growth will be green hair. If you start getting purple cyano on the screen, it means your light is too weak or too far away. If you start getting a hard yellowish plastic-like coating that covers the algae, it means your flow is too low in that area. If you start getting bald spots near your bulb, it means you are leaving your bulb on 24 hours, when you should be turning it off 6 hours a day. If you start getting round holes in your algae, it means pods are eating through it, because you are not using freshwater in your 7-day cleanings.