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Five Things to Know About Algae

Unless it’s St. Patrick’s Day, it’s no fun to see a bright green swimming pool. Check out Groupon’s intro to algae to understand why addressing it will always keep pool-cleaners busy.

1. There are tens of thousands of algae in the world, but pool-owners usually only have to worry about a few. Most obvious is the green, free-floating stuff known as chlorophyta, but there’s also yellow or algae that creates an oily film on walls. Worst is a black or blue-green algae with a protective outer layer that can dig deep into grout and plaster and give pool floats mange. A fourth common pool complaint, called pink algae, is actually a bacteria that enjoys cuddling up to PVC surfaces. In all cases, a combination of intensive scrubbing, sanitizing, and chlorination can typically treat the problem.

2. Algae isn’t bad for you—on its own. While the worst effect of an encounter with algae is likely to be a slimy swimsuit, it can be a sign that other forms of trouble are afloat. If algae appears suddenly, it’s likely that the pH level of your pool has changed from heavy use, rainwater, or your neighbor secretly borrowing a few gallons and replacing it with Crystal Pepsi. That can set the stage for invaders such as dangerous bacteria to find their way in.

3. Algae aren’t plants or animals, exactly. For a long time they were classified as plants—and they do make their own food through photosynthesis—but actually, algae don’t reproduce as plants do, and they lack key features such as stems, roots, and a sense of style. The group is hugely diverse, ranging from single-celled organisms to giant kelp that can grow a foot per day until they’re nearly 200 feet long.

4. When it comes to chlorination, the magic ratio is 3:1,000,000. That’s the concentration chlorine needs to reach in water to prevent algae growth. If it gets diluted, normal conditions can be restored by “shocking” the pool with a more intense dose of chlorine until the water turns a cloudy blue or gray—the color of a dead algae army.

5. One day, algae might fly your plane. Biotech companies are currently working to create super-algaes that can synthesize certain oils—which can then be refined into diesel and jet fuel.