Skip to main content


Browse Our Resources

Tags: Inground Pools, Pool Chemicals, Pool Service

Why Is There Algae in My Swimming Pool?

March 17, 2017

Algae is a one-celled plant that can grow in your pool if conditions are favorable, and it’s a major concern for swimming pool owners. The most common reason for algae growth in pools is that it has a low chlorine (or its alternative) in the pool. Although this is definitely a major cause of algae, it is not the single contributing factor.

Why Is There Algae in My Swimming Pool?

Despite water treatment facilities best efforts to remove all impurities from the water supply, actual traces of algae may very well be present in the tap water that is used to fill your pool. Another contributing factor to algae growth in pools are the millions of microscopic algae spores that are carried by wind, eventually falling into your pool. These spores will grow into outbreaks of algae if conditions are favorable.

The main reason you have algae or faint green coloring, is that you more than likely forgot to check your chemicals or do standard swimming pool services.

What Kind of Environmental Conditions are Favorable to Algae?

Algae, like all plants, need light and food in order to survive and grow. Temperature, humidity, sunlight, and nutrients (food) foster algae growth. And, your backyard pool offers 3 or 4 components for algae to flourish. Algae get their nutrients from products like lawn fertilizers and other industrial products that are carried by wind and blown into the pool. Nutrients also consist of certain minerals that are already present in water. Since water chemistry relies on some of these certain minerals to be present, they cannot simply be removed from the water.
Here is a possible sequence of events: Algae spores will blow into your pool, where they are supported by temperature, humidity and sunlight. The algae spores then consume various nutrients (phosphates). From temperature, humidity and sunlight, as well as from nutrients, the once unnoticeable algae spores have now grown into actual algae.

Poor Pool Filtration and Maintenance Also Lead to Algae Growth

In addition to these environmental factors there are other factors related to pool chemistry and pool equipment. Things like:

  • Poor or limited water circulation
  • Poor pool filtration systems
  • Neglected routine swimming pool services
  • Heavy bather loads
  • Neglect of “shocking” the new water supply
  • Neglect of overall water chemistry
  • Insufficient levels of chlorine (or its alternative)

How You Can Control Algae Growth in Your Pool

Algae causes the appearance and integrity of your pool to suffer and occupies time to correct. If you do get algae, you are not alone; it has been seen in pools of some of the foremost authorities on pool care and maintenance. Rest assured, any algae can be killed, but not without a few days of continued effort and time.

The main thing is to maintain properly water chemistry with proper circulation.  Keep your chlorine level up to where it is supposed to be and that will eliminate many of your algae outbreaks.

Quick, Easy Ways to Kill Algae in Your Pool

It is best to begin with the necessary steps to prevent algae growth. Our general rule is: an ounce of prevention is worth a hundred pounds of cure.

  1. Vacuum your pool to waste to get rid of any algae on the pool floor.
  2. Brush your entire pool, including rails.
  3. Adjust the water to the correct pool chemistry.
  4. Shock your pool.
    1. If you can see the deep end of your pool, do a double shock.
    2. If you can’t see the deep end, do a triple shock treatment.
    3. If you can’t see the shallow end, do a quadruple shock treatment.

We recommend that when your fill or refill your pool for the pool season, that you shock your pool. Shocking your pool means adding extremely high levels of chlorine (anywhere from 3 to 5 times the normal amount) to the pool for a short period of time. Shocking helps eliminate algae and bacteria; we recommend shocking as close to dusk as you can to limit the sun from changing the chemical composition.

Now you know a little more on Why Is There Algae in My Swimming Pool?; and how to simply get rid of it. Remember that simple swimming pool services for your pool will eliminate many of your pool issues.