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 While the majority of the information presented here is still correct, there are a few things that are outdated.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!
Cleaning the screen
Cleaning the screen should be done remote from the tank. A common complaint of the past was that an Algal Turf Scrubber turned the water yellow, but that was because algae was generally removed from the tank with the screen in place, or it wasn’t well rinsed.
If you have lots of pod-eaters in your tank, and your screen is nice and green (no slimy growth) you can consider swishing the screen in the tank every once in a while before cleaning. I did this a few times, but I really don’t anymore.
Screen cleaning should be done in room temperature tap water. The reason is that freshwater kills pods that are continually munching on the screen. There will be millions more in no time, you just don’t want them causing algae to detach between cleanings.
I use a cutting board and a plastic pot scraper similar to this one https://www.pamperedchef.com/ordering/prod_details.tpc?prodId=241&catId=9 to scrape the algae off the screen.
You will need to use an old toothbrush or a stiff-bristled scrub brush to remove any algae that grows on the smooth area at the top of the screen. I also use a scrub brush to remove any red turf. Red turf seems to grow well in the lower light areas. I have since trimmed these areas off the screen since I needed to make it smaller.
The slot tube also should be cleaned by scrubbing with a brush and rinsing. If you have an enclosed box device, you will likely need to clean algae out of there occasionally too. I have to do this every cleaning, it’s amazing how well algae attaches to a smooth surface.
After all the scraping and scrubbing is done, give the screen a good rinse (15-20 seconds) in fast running water.
For the first 4-6 weeks, cleaning every 7 days is probably a good idea (see the ‘Screen Break-in Period’).
The exception is the ultra-high nutrient system that results in a black slime coating forming every 2 or 3 days. Such growth must be completely removed, as soon as possible - at the most every 3 days (see “Algae Growth Types”)
The general rule has been to clean your screen every 7 days. This is still the rule for single sided and non-vertical Algae Scrubbers.
If you run a double-lit vertical Algae Scrubber, now it is allowable to let the screen grow as long as 10, and in some cases, 14 days. Again, you need to pay attention to your screen growth, and that it as simple as checking it once a day, because the frequency of necessary cleaning relates to what kind of growth you’re getting.
I nice, thick mat of emerald green hair algae does the best filtering.
Regardless of growth type, as the algae mat grows thicker, the outer layers block light (and flow) to the lower layers, specifically where the algae attaches to the screen. This causes weakening of the strands, which can lead to algae detaching from the screen. This is more likely to happen with a single-sided screen, because the light intensity less at the screen level. It is less likely to happen in an enclosed-box 3D growth type system, as the algae is supported a little better.
What really tells the story is what the algae mat looks like when you clean it. If you are regularly cleaning off a thick mat of green algae that is firmly attached to the screen, you can probably let this go for a few more days between cleanings. Increase by one day at a time and monitor closely. If the algae becomes a lot easier to clean off, or becomes straw-like near the screen, this means the algae in the lower layers is not getting enough light and/or flow, and is dying, and you’ve reached (or possibly exceeded) the limit on how long you can go between cleanings.
If you are getting a thin layer of algae, but it’s not too dark (maybe a darker green or thin and brown, and you can still see the screen) you can let the screen grow for a few more days. The key here is that as long as light is penetrating all the way down to the algae attached to the screen, you can let it grow. You want to allow the green algae, however much you are getting, a chance to grow.
If you are getting a little thicker mat of brown growth, don’t go over 7 days. Same goes for the yellow, rubbery growth. You can clean these more frequently than 7 days; try to leave as much green hair algae that you have on the screen. If you are getting black, slimy growth, clean about every 3 days.