Why is my pool green and how to clean it?

Having a pool at home is great most of the time because swimming in it provides you with the opportunity to cool off. Other times, especially when there is no pool cleaning routine, bathing time may be disturbed by the aspect of water, not so crystal clear as usual but rather green, and from its tone, we may sense the level of neglect.

In most cases, the green shades indicate the presence of algae in a pool. Water is such a fluid element that any change in its composition can turn it into a suitable environment for algae growth. This is a fact that is important to be aware of since a pool with a lot of algae can be a health hazard.

Perhaps most cases of green pool water indicate the presence of algae; however, the cause of algae growth is not always the same. The first thing you have to do when observing green tones in your pool is to test the water. As mentioned above, changes in water composition or chemical imbalances may lead to the growth of algae for many reasons, let’s review the aspects of water that need to be inspected:

Find out your home's credit score

Check your home condition score to find out!

Check it out

Alkalinity levels

The alkalinity test consists of measuring the alkaline substances present in water, hence it is measured by parts per million. Regarding swimming pools, the recommended alkalinity levels range from 100 to 150 PPM. Usually, this measurement is correlated with pH, since when the water alkalinity is high, the water pH is also high, and vice versa. Therefore, its treatments could be the same in some cases. However, you must bear in mind that they are two different aspects, and their measurements provide us with different kinds of information.

pH levels

The pH measurement will tell whether a substance, in this case, water, is basic or acidic on a scale from zero to fourteen. When it comes to swimming pools, the recommended pH for water ranges from 7.4 to 7.6.

If our pool water is below this range, it means that it is acidic, and the free chlorine levels of our pool might be low, therefore, shock may stabilize these levels. On the contrary, If the pH is above this range, we should not add more chlorine to the pool, since a high pH decreases the effectiveness of chlorine and may cause eye or skin irritations. In these cases, it is recommended to use a pH reducer or muriatic acid.

Phosphate levels

When testing pool water, it is also important to measure its phosphate levels. They may be the cause of cloudy and green tones in our pool water as high levels of phosphate make water a suitable environment for algae. For these cases, there are phosphate removers exclusively for pools available on the market.

Free Chlorine levels

When having a pool, it is important to keep track of its chlorine levels regularly. Chlorine is an essential compound for swimming pools, as it prevents algae growth and keeps our pool sanitized. Some experts advise that a pool’s free chlorine level should range between two and four parts per million. Once this level decreases, it is required to shock again the pool with chlorine.

When our pool water is green, the shock is what will kill algae and may raise pH. During this process, it is recommended to use 1 lb of Chlorine per 10000 gallons of water, however, these amounts may vary depending on the shade of green our pool is. The greener and darker the pool, the more chlorine we will require.

In addition, it is advisable to perform the shock at night since the sun may burn the shock and may diminish its effectiveness. Also, use a brush for the walls and floor of the pool, this will help the shock to accomplish its objective of sanitation.

Once the free chlorine levels have stabilized, remember to balance them by testing the water once a week. Keeping the free chlorine balanced will maintain our pool crystal clear for swimming.

Besides chemical imbalance, there is one last item that might be causing the green shades in our pool water: the filter.

Pool filter

As you shock your pool, you must also sanitize the filter, this will allow fresh and clean water circulation within the pool. After sanitizing, run the filter for 8 hours to test the water again. Be aware of the filter functioning since poor water filtration may be the cause of algae. If on the next day, the water test does not present the expected results, you should shock your water again and filter it for another 8 hours.

If after the second shock, your pool is still green or the composition of your water has not stabilized yet, there is probably a problem with the filter. Remember that if the filter does not run long enough, it may need a replacement.

Now that we have reviewed the aspects that may be turning your pool water green, your must take your time to measure water composition and also to shock your pool. You may be excited about a fresh bath, but the process of turning your water clean and fresh again may take time. So, focus on making your water suitable for you, at the end, this will be rewarded with a clean and relaxing bath.

If after many tests and shocks, the water in your pool is still green, it is recommended to call a pool expert. They will help you find out if there is major damage to your pool.

Written by Billy Guteng. May 1, 2023

Billy was born in France, and has lived in multiple cities around the world ever since. He loves art, design and architecture and he supports the KUKUN team as a content provider.