If you’ve noticed your swimming pool water turning an inky, dark blue color, you may be wondering what’s causing this change. A few different factors can lead pool water to become dark blue, but the most common culprits are heavy metal contamination and algae growth.
Heavy Metal Contamination
Certain heavy metals like copper and iron can tint pool water a deep, dark blue if they build up to high levels. Here are some ways heavy metals can get into your pool and what to do about it:
Pipe Corrosion
Over time, the metal pipes and fittings used in pool plumbing can corrode. This releases copper, iron, and other metals into the water. Replacing old, corroded pipes and fittings is the best way to stop this.
Well Water
If your pool is filled using well water, dissolved minerals like iron and manganese can be present at high levels, causing blue-green staining. Using a stain and scale inhibitor can help prevent metals from staining the water.
Metal-Based Algaecides
Some algaecides contain copper compounds. As these dissolve, copper builds up which can turn water blue. Switch to a non-metal based algaecide to avoid this.
Metal Pool Surfaces
In pools with metal walls or bottoms, like galvanized steel, corrosion can leach iron into the water. This is difficult to control. Consider re-plastering with a non-metal surface.
Removing Heavy Metals
| Method | How It Works |
|---|---|
| Chelating agents | Bind to metals to prevent staining |
| Metal filters/removers | Filter out dissolved metals |
| Sequestrants | Keep metals dissolved in water instead of staining |
| Metal precipitators | Chemically convert dissolved metals into solid particles that can be filtered out |
Algae Growth
Certain types of algae can also cause pool water to turn dark blue-green when they start to bloom. Common culprits include:
Mustard Algae
Also called yellow or brown algae. Mustard algae grow on pool walls and floors, leaving behind a yellowish, mucus-like film. The water turns greenish-brown or bluish-black when a large amount is present.
Black Algae
Black algae grow in small black spots on surfaces and can leave black streaks on walls as it washes off. It turns water extremely dark green or blue-black at high levels.
Controlling Algae
To prevent algae from turning your pool water blue, it’s essential to maintain proper pool chemical balances. Here are tips for keeping algae growth in check:
| Method | Details |
|---|---|
| Chlorine | Maintain 1-3 ppm free chlorine to kill and prevent algae |
| Shock | Shock treat weekly and after heavy bather loads |
| pH | Keep pH 7.2-7.6. Low pH stops chlorine from working properly |
| Algaecides | Use preventively according to label directions |
| Circulation & Filtration | Run filter enough hours daily to turnover all water 1-2 times |
| Brushing | Brush walls and floors weekly to remove growths |
When to Call a Pool Professional
If your efforts to remove heavy metals or control algae growth don’t restore the water to its normal clear, blue color, it’s a sign there is an underlying issue that needs professional attention.
Pool pros have specialized equipment and chemicals to measure and correct water balance issues. They can test to identify and treat specific metal contaminations or persistent algae. Severe stains may need additional treatments like gel-stain removers or acid washing.
Don’t let unexplained blue water go untreated. The longer imbalance issues persist, the more engrained and difficult to remove they become. Contact a pool company promptly if you’ve been struggling with blue, green or black water.
Preventing Blue Water
Once you’ve got your pool water clean and clear again, be diligent in your maintenance to prevent a recurrence of blue green staining. Here are some tips:
- Test water 2-3 times per week and adjust chemicals as needed
- Shock weekly to control algae and bacteria
- Check and replace old metal components proactively
- Clean filtration equipment regularly for maximum effectiveness
- Brush surfaces thoroughly each week
- If using well water, have metal levels tested annually
- Drain and refill periodically to dilute dissolved contaminants
Conclusion
A variety of issues can cause your pool water to turn an unattractive and worrisome blue-green color. By understanding the common causes, like metal staining and algae growth, you can take steps to restore proper water balance and clarity. If DIY efforts don’t do the trick, don’t hesitate to call in a pool professional for their expertise and access to specialized diagnostics and treatments. Consistent maintenance and monitoring will help keep your water pristine and avoid any mysteries with blue pool water cropping up again in the future.
