Cleanings are when you take the screen to the sink and run tap water over it as you use your fingers (not fingernails) to remove the loose stuff and wash it off. It is done everyweek, no matter what, even if you think your screen needs to "grow more first". On brand new screens, this stuff is usually a light brown slime, but it can be green slime, green hair, or even black tar-looking stuff. It's important, especially on the first cleaning, to leave some algae on the screen so it can grow back easily. It's also important to only clean ONE side per week (or one-half, if it's a one-sided screen). Cleaning it under running tap water kills the pods that will start to eat the algae (don't worry, there will be thousands more the next day).

Scrapings are sometimes needed later on, after your screen has grown a few months. You'll know if scrapings are needed: You'll try using your fingers, or even fingernails, but nothing will come off. Scraping is only needed every month or so, and of course on ONE side only (or one-half, if it's a one-sided screen). I use a razor blade to scrape, but any straight sharp metal object will work. Go back and forth with the scraper until the algae is removed all the way down to the screen. You shouldn't have to worry about leaving algae on the screen; this type of algae is tough enough that there will surely be some left. You may never need to scrape, however, which is fine. But even if you do need to scrape monthly, you'll still need to clean weekly.

Here is a video showing a cleaning and a scraping:



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