Why is my pool green?

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If you own a pool, chances are you’ve had moments where an unsightly green tint catches your eye—why is the pool green?! And as luck would have it, it’s usually before a big event or pool party. Don't panic—pool owners everywhere deal with the frustrating issue of green pool water at some point. Fortunately, the causes and solutions are usually easy to pinpoint, and that’s the biggest step back to crystal-clear pool water. Keep in mind, however, that fixing a green pool requires an expert touch — someone with the knowledge and tools to assess, remedy, and prevent the situation.

Algae and green pool water

Green pool water is almost always caused by an algae infestation. Algae are simple organisms found in various aquatic environments — including your pool! Algae can appear in a variety of colors, but most often, those that bloom in your pool are green or yellow. In addition to giving your pool a green or yellowish tint, you may notice that the water seems murky.

While algae are not inherently harmful to humans, they can create unsightly and potentially hazardous conditions in swimming pools. Some types of algae can make surfaces slippery and pose slip-and-fall hazards. They thrive in warm, sunlit conditions and can reproduce rapidly.

Why algae grow in a pool (and how to fix a green pool)

There are a handful of reasons why algae may proliferate in your pool and turn it green (in short order!). Sometimes, it’s a combination of factors.

Too much sun.

Algae love sunny, warm environments, so you may notice more struggles with your pool turning green in hotter months. Limiting sunlight exposure can help prevent algae growth. Consider installing a pool cover or using shade sails to reduce direct sunlight exposure to your pool water.

Too much rain.

You may be wondering, “Why does my pool turn green after it rains?” Heavy rain is the perfect storm (pun intended) for algae growth because it dilutes the pool chemicals (like chlorine) that keep algae growth at bay; it carries various organic contaminants like pollen and algae spores into your pool; it can be acidic, which can cause an imbalance of pH levels that reduces the effectiveness of chlorine and creates favorable conditions for algae growth; and finally, rain and storms can cause debris and sediment to settle at the bottom of your pool, obstructing water circulation (which, you guessed it, encourages algae growth).

While you can’t prevent the rain, you can be proactive about balancing the necessary chemicals immediately after the rain to prevent algae growth in the coming days.

Imbalanced pH levels.

Fluctuations in pH levels can create an environment conducive to algae growth. If your pool water's pH is too high or too low, it can hinder the effectiveness of chlorine, allowing algae to flourish. Test your pool water regularly and adjust the pH levels as needed using pH increasers or decreasers. Aim for a pH level between 7.2 and 7.6 to keep your pool water balanced and resistant to algae growth.

Insufficient or ineffective chlorine levels.

Algae can grow if chlorine levels are not adequate (this includes saltwater pools, too!). If chlorine is high but your pool is green, this can be because the chlorine is not effectively combating algae. This can occur if the chlorine is bound to contaminants or if the pool water's pH is too high.

Maintain proper chlorine levels in your pool by regularly testing and adjusting the chlorine concentration as needed. Shock your pool with chlorine to break apart chloramines and eliminate algae.

Insufficient filtration and circulation.

When the filter is blocked or circulation is poor, algae can thrive. Invest in a high-quality filtration system and ensure proper pool water circulation to prevent algae growth. Run your pump and filter regularly to keep the water clean and clear. You can also consider installing a UV filter, which is highly effective at killing algae spores and other bacteria before they have a chance to bloom.

Fix a green pool fast

Preventative measures have failed, and your pool is GREEN. Don’t panic—solving the issue is usually as simple as shocking your pool with a high dose of chlorine to kill existing algae. Follow up with an algaecide treatment to prevent regrowth. You may also need to brush the sides of your pool to dislodge algae spores. You may notice that this causes your pool water to look murky. Be patient—your pool filter will work over the next 24-48 hours to create a clearer appearance.

Preventing a green pool

As mentioned, the key to preventing a green pool is to hire an expert who can provide consistent maintenance. As a pool owner, you can do your part too:

  • Establish a routine cleaning schedule that includes skimming the surface, brushing the walls, and vacuuming debris.
  • Stay on top of rain and weather changes — and call your pool maintenance company at the first sign of an issue.
  • Ask your pool maintenance company about the latest technologies and tricks (like the aforementioned UV filter) to prevent a green pool.

At White's Pools, we’ve been delivering top-tier pool maintenance services in Atlanta for more than 75 years. In fact, as a family-owned company, we’re on our fourth generation of pool experts—so we know a thing or two about fixing and preventing a green pool. By understanding the causes behind green pool water and implementing effective solutions and preventative measures, we’ll help you keep your backyard oasis sparking! Request a pool maintenance quote today.