This… is yellow algae

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This… is green algae

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This… is black algae

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The differences are subtle.

Yellow algae starts to form on the walls of your pool and can be easily brushed away with your hand. It has the color of a blade of grass.

Solution: Raise pH to >7.8 and add Yellow Out and shock. Or use Algae Solution and shock.

Green algae infects the water very fast and is a forest green color.

Solution: Drop the pH to 6.8 and raise the chlorine level to >30ppm.

Black algae is tricky. Sometimes it looks black but it can look yellow or green. Black algae doesn’t infect the water and doesn’t brush off easily.

Solution: Silvertrene and a stainless steel brush if it’s widespread. If it’s just in a few spots you can grind a chlorine tablet into it.