What Causes Algae?

Algae spores are everywhere. These microscopic single-cell structures are blown into the pool by the wind, washed into the pool by rainfall, or carried into the pool on swimmers’ skin or bathing suits. Under the right conditions, tiny spores will bloom into those dreaded bright green, mustard yellow or black discolorations.

Inadequate filtration will often lead to algae growth.

Water clarity depends on daily circulation and filtration. Anything that impedes water flow from the pool to the filter — clogged skimmer baskets, a dirty or damaged filter, a defective pump motor, or a failure to run the pump for an adequate amount of time each day — will encourage algae growth. The first warning sign of a filtration problem is hazy or cloudy water. Left unchecked, cloudy water can quickly lead to a full-fledged algae bloom.

Algae can develop when little or no chlorine is present.

Sunlight, rainfall, temperature, number of swimmers and frequency of pool use affect the rate of chlorine loss. The lower the chlorine level, the more likely algae will bloom. Super-chlorination, coupled with the application of conditioner or stabilizer designed to shield residual chlorine from the effects of heat and sunlight, helps ensure that there is always sufficient chlorine in the pool. Spas, which are often heated to temperatures well above 100 degrees, are especially susceptible to algae growth.

Algae loves a dirty pool!

Leaves and dirt left on the bottom of the pool for an extended period of time, not only promotes algae but also causes pool staining. The longer you allow leaves and other debris to sit on your pool floor, the more likely that you’ll see algae, and staining. In a dirty pool, algae will continue to bloom, even when the water chemistry is properly balanced.