If you have a swimming pool, you probably know how important it is to maintain the water chemistry and keep it clean and clear. However, sometimes you may notice that your pool water turns green, even if you have high chlorine levels. This can be very frustrating and confusing, as chlorine is supposed to kill algae and bacteria that cause green water. So, what is going on?
The Role of Alkalinity in Pool Water
One of the possible reasons why your pool is green but chlorine is high is that your alkalinity level is too low. Alkalinity is a measure of how well the water can resist changes in pH. It acts as a buffer that helps keep the pH stable and within the ideal range of 7.2 to 7.8.
Why is pH important? Because it affects the effectiveness of chlorine and other sanitizers. If the pH is too high, above 7.8, the chlorine becomes less active and unable to kill algae and bacteria. If the pH is too low, below 7.2, the chlorine becomes too aggressive and can damage the pool surfaces and equipment.
Low alkalinity can cause the pH to fluctuate and become too high or too low. This can create an environment where algae can grow and thrive, despite the presence of chlorine. Low alkalinity can also cause corrosion, staining, scaling, and cloudy water.
The Causes of Low Alkalinity in Pool Water
There are several factors that can lower the alkalinity level in your pool water, such as:
- Rainwater: Rainwater is acidic and can dilute the alkalinity in your pool.
- Evaporation: Evaporation can concentrate the minerals in your pool water and increase the pH, which can lower the alkalinity.
- Chemicals: Some chemicals, such as muriatic acid or sodium bisulfate, can lower the alkalinity when used to adjust the pH or other parameters.
- Bather load: Bather load can introduce organic matter, such as sweat, urine, cosmetics, or sunscreen, that can consume the alkalinity in your pool.
- Algae: Algae can consume carbon dioxide from the water, which can increase the pH and lower the alkalinity.
The Solutions for Low Alkalinity in Pool Water
To prevent low alkalinity from causing green pool water, you need to test your water regularly and adjust it accordingly. Here are some steps you can take to fix low alkalinity and green pool water:
- Test your water: Use a reliable test kit or strips to measure your alkalinity, pH, free chlorine, and cyanuric acid (CYA) levels. You should aim for an alkalinity level of 80 to 120 ppm, a pH level of 7.2 to 7.8, a free chlorine level of 1 to 3 ppm, and a CYA level of 30 to 50 ppm.
- Raise your alkalinity: If your alkalinity level is below 80 ppm, you need to raise it by adding baking soda or sodium bicarbonate to your pool. Follow the instructions on the product label or use an online calculator to determine how much you need to add based on your pool size and current alkalinity level.
- Lower your pH: If your pH level is above 7.8, you need to lower it by adding muriatic acid or sodium bisulfate to your pool. Follow the instructions on the product label or use an online calculator to determine how much you need to add based on your pool size and current pH level.
- Shock your pool: If your free chlorine level is below 1 ppm or you have visible algae in your pool, you need to shock it by adding a superchlorinated shock treatment. Make sure to use a chlorine-based shock product that contains at least 65% calcium hypochlorite or 70% sodium dichloro-s-triazinetrione. Follow the instructions on the product label or use an online calculator to determine how much you need to add based on your pool size and current free chlorine level.
- Clean your pool: After shocking your pool, you need to clean it thoroughly by vacuuming, brushing, skimming, and backwashing or rinsing your filter. This will help remove any dead algae or debris from your pool.
- Test and balance your water again: After cleaning your pool, you need to test and balance your water again. Pay special attention to pH, alkalinity, and chlorine levels. You may need to repeat some of the steps above until you achieve clear and balanced water.