The algae spores are in the air, and if enough of them end up in your pool, you get mustard algae. Pools that have high levels of sanitizer (chlorine) also get mustard algae.

Getting mustard algae is kind of like getting the flu. The algae spores are in the air, and if enough of them end up in your pool, you get mustard algae.

Learn More › Black algae in a pool is not just unsightly. Although it isn’t harmful itself, it can spread rapidly and harbor dangerous bacteria, like E. coli, that can make swimmers sick.

“When your pool turns green, everybody knows when your pool turns green, that’s not good to swim in.” Your pool’s pH or acidity level should be between 7.4 to 7.6.

My pool man agreed that we should give it a shot. I had some 30 percent peroxide product left around from a previous project, so I put 3 gallons of the concentrated hydrogen peroxide in the water ...

A: It sounds like your pool has the color and texture of chicken soup, and I’m sure it feels icky to swim in it. Therefore, you must have yellow algae (aka mustard algae), and you can clear it ...

Answer: This pool could still have algae even with the water testing fine. It may have mustard algae, which brushes off in a cloud of dust, or a resistant strain of green algae.