Please note: This is the version that was posted online in early 2012. While the majority of the information presented here is still correct, there are a few things that are outdated. I've been meaning to update this for quite a long time, if you have any questions, you can click the Discussion tab and ask!
Screen Break-in Period
Since the time frame by which you will see certain types of growth largely depends on the bio-load, initial nutrient conditions of the system, and strength of the scrubber, not everyone will see the same growth progression. Some have taken months to get a full screen of green growth; others get great results in just a few weeks. However, every screen must go through an initial break-in period, and that is relatively independent of anything else. Usually, the first week or two of growth is almost identical for any scrubber; after that, different system will tend to diverge depending on the conditions.
When you first start up your algae scrubber, even with the screen significantly roughed up, it is still relatively slick on a microscopic level. It is plastic, after all. The reason behind roughing up the screen is to vastly increase the surface area, and to give long strands of algae something to hold on to.
As the tank water cascades over the screen, there will initially be a buildup of brown slime, similar to what you see on the insides of your tank plumbing (and like what you clean out of your pump). Over time, this growth on the screen will strongly adhere to the screen. The bond is so strong that you would have to soak the material in vinegar to completely remove the algae. This may sound familiar to anyone running pumps or powerheads (which should pretty much include everyone).
During the break-in period, this brown layer is easily rinsed away (with a sink sprayer, for instance). For the first few weeks, a very light cleaning is all that is needed – just lightly running tap water. A gentle swipe of your fingertips will take most of this layer off, but will leave enough behind that if you put a new screen next to it for comparison, you will see a slight color difference. You want to leave behind anything that doesn’t easily wash away, including whatever is growing in the holes. You definitely don’t want to scrub the screen with a brush of any kind. Any growth you get for the first few weeks should be easily removed with your fingertips (not nails). If you happen to get some long green hair algae strands, you should be able to remove those with your fingernails (gently).
Usually after the second cleaning, the screen will have developed a foundation upon which algae will be able to form a good bond. What type of algae will grow next is dependent upon factors stated in the first paragraph of this section. Regardless of the type of growth, the screen will continue to mature to the point where if and when a thick mat of algae grows, it will stay firmly attached to the screen. This is usually attained around the 4-6 week point, and can be verified when algae grows inside the ‘squares’ of the screen and does not come loose during cleaning.
My screen break-in cleaning technique progressed as follows:
Week 1: Rinse with slow running tap water
Week 2: Same, except used fingertips to rub screen
Week 3: Rinse off with running water, then rub with fingertips
Week 4: Same
Week 5: Same, had to use backs of fingernails in some places
Week 6: Algae firmly attached. Used back of fingernails across entire screen (now I use a plastic scraper)
Every scrubber will have slightly different growth progression, but the guideline above gives you an idea of what to expect. See “Algae Growth Types” for some additional information.