Walked outside ready for a swim only to discover that your pool looks like pea soup? In most cases, pools shouldn’t be green, unless that’s the color of the lining. Cloudy green water is usually a sign that something is majorly wrong. In this post, we’ll explore some of the possible causes and offer some tips on how to turn your uninviting green swamp back into a crystal clear blue oasis.

swimming pool

Why do pools turn green?

Pools can turn green for a variety of reasons. Algae growth typically plays a part, but there can be root causes behind this. Below are some of the main reasons a pool might start to look cloudy and discolored:

Algae overgrowth

Algae is a plant-like organism that grows in all kinds of water. It particularly thrives in warm water exposed to direct sunlight. Poor circulation can also encourage algae growth.

At first, as algae takes hold, the water might appear a light green color. This can eventually develop into a dark green, murky color as the algae multiplies.

You should never swim in a pool that contains algae. This is because algae creates a harmful breeding ground for bacteria, which can cause people to develop skin rashes and eye/ear infections. Algae can also stain the surface of your pool – especially if left to become  thick and slime-like. 

Low chlorine levels

Most pools are chlorinated and this chlorine helps to kill off algae. If chlorine levels drop too low, algae can start to develop. At first the water may turn dull, and then it will start to take on a green color.

If lots of people are using your pool regularly, the chlorine levels will naturally drop. Direct sunlight can also break down chlorine, while heavy rain can dilute your pool.

High pH levels

Even if you’re adding chlorine, it won’t work properly if the pH level of your pool is too high. 

The ideal pH level of a pool is 7.2 to 7.6. If it rises above this range, expect the pool to start getting cloudy. The alkalinity of the water could also start to irritate your skin and eyes.

Rainfall, sweat and sunscreen can all increase the pH level of a pool over time.

High copper levels

That green tint to your pool could potentially be caused by metal oxidization as a result of copper dissolving in your pool. 

This could be the result of corroded plumbing or metal fixtures within your pool – potentially caused by low pH (high acidity) of water. Alternatively, if you’ve been using algaecides on your pool, some of these may contain copper.

Unlike algae which will make your pool a cloudy green color, copper exposure is more likely to result in clear light green water. 

Other causes of cloudy or discolored pools

Beyond turning green, pools can become cloudy and discolored for a variety of other reasons. This includes:

  • Pollen: Pollen dust can sometimes create a yellowish green layer on the floor of a pool.
  • High calcium levels: If calcium levels are too high, the water may turn a cloudy white color.
  • Low pH: A low pH can also lead to cloudy water.
  • Dirt: Sand or mud can cause a pool to become a cloudy gray or brown color.
  • Debris: Debris like twigs, leaves and grass can all change the color of a pool.

How to fix a discolored or cloudy pool

Because the cause of a discolored pool is not always obvious, you may need to take a few different steps to solve the issue. 

Step 1: Test the water

Use a test kit to check if the chemistry is off. Test kits and test strips will be able to measure the chlorine, pH, alkalinity and calcium levels. 

Step 2: Adjust pH first

A high pH level tends to be the culprit in many cases. If it’s above 7.8, use a pH reducer (such as dry acid or muriatic acid) to bring it down. If it’s below 7.0, you’ll need a pH increaser. The perfect pH level is between 7.2 and 7.6.

Step 3: Raise the chlorine

Once pH is in range, it’s time to hit the algae hard. Shocking the pool is recommended – this involves adding a high dose of chlorine to wipe out the algae. After this, you’ll want to brush the wall, steps and floor. As the algae dies, the water should turn from a green color to a cloudy white.

Step 4: Run and clean the filter

Your pool’s filter will help to remove all the dead algae, however if there was a lot of algae in your pool, you could find that it gets clogged. Cartridge filters should be rinsed thoroughly after filtration is complete. If your filter is old and not working very well, consider replacing it.

Step 5: Consider using a clarifier

Pool clarifiers are specialist chemical products that can help to remove all kinds of particles from your pool from pollen to dirt. They cause tiny particles to bind together into solid clumps that can be more easily removed by your filter. Clarifiers can often help to get rid of copper residue if this is a culprit. Just be wary that clarifiers may not always solve the issue.

When to bring in the pros

If you’ve tried all this and your pool is still cloudy (or, worse, still green) it might be worth looking into a professional pool service to check and clean your pool.

Professional pool cleaners will be able to carry out a deep clean and rebalance all chemicals. They can also look at equipment like filters to see if they are the problem.

How to prevent you pool going green again

To prevent your pool going green again, make sure to test the water 1 to 2 times per week. Keep chlorine and pH at recommended levels and run the pump and filter for several hours each day. Cleaning out any debris on a regular basis (or using a pool cover when not in use) will also help to keep your pool crystal clear and inviting.