If your pool water looks murky, green, or cloudy, this could be a sign of algal growth. During high-temperature months, algae infestations become very common, especially if there’s an imbalance in your pool’s chemistry.
If you suspect your pool has become home to these microscopic green plants, don’t worry. Below, we’ll explore how to test, remove, and prevent algal growth in your pool.
If your water appears cloudy for other reasons, be sure to read our guide on how to clear cloudy pool water fast.
How to Know if There’s Algae Growth in the Pool
Even a small amount of algae suspended in water will make your pool appear cloudy and dirty. If you suspect an algae growth in your pool, feel the side of the pool with your hand. If algae are to blame, the pool sides will feel slippery.
Another way to test for algae growth is by performing an overnight chlorine loss test (OCLT). Add chlorine to pool water in the evening when the sun is down. Take a Free Chlorine (FC) reading the following morning before the pool gets hit by direct sunlight.
If the levels remain the same, you do not have any organisms growing in the pool. If the level drops by more than one PPM throughout the night, this confirms you have algae growth in your pool.
How to Remove Algae From Your Pool
Removing algae from your pool can be slightly complicated, especially if it’s been there for too long.
First, ensure your pool’s circulation, filtration, and sanitation systems are all working. Then follow the steps below to remove algae from your pool.
- Scrub the walls and floor of your pool using a pool brush to loosen and remove as much of the algae as possible. Scrub every nook and cranny–use nylon brushes for vinyl pools and steel brushes for concrete pools.
- Next, check the pool’s pH using a pool pH testing kit. If the pH is above 7.6 (as is common in an algae bloom), use a pH reducer such as sodium bisulfate to reduce the pool pH to between 7.2 to 7.6. Wait two or three hours before testing the pool water again.
- Now it’s time to add chlorine shock treatment to your pool water. Wait until after the sun sets to shock your pool so the UV rays don’t break down the chlorine. Dissolve the shock treatment in a bucket full of water and pour it as close as possible to the algae.
Use about twenty grams of shock treatment for every 500 gallons of water in your pool. Keep your filter running after adding the shock treatment so it continues to cycle through the water. If the algae has a dark black or mustard-yellow appearance, double the shock treatment to make it more effective.
- When shock-treating your pool, make sure to follow these safety instructions:
- Cover your skin and wear gloves and eye protection whenever handling chlorine products.
- Avoid swimming in your pool for two to three days after shock treatment or until the chlorine level has returned to three PPM. High chlorine levels can irritate your eyes and skin.
- Test the pool’s pH and chlorine levels again the next day, and adjust depending on your measurements. Check if your pool has dead algae, which will look like gray or brown matter floating in the water or settled on the pool floor.
- It’s crucial to keep testing and maintaining your pool water chemistry every week to prevent the algae from regrowing. Test the chlorine levels, alkalines, pH, and cyanuric acid daily for the next one or two weeks to ensure they’re at a reasonable level. The faster you catch a problem with the pool chemistry, the easier it will be to correct before algae grows again.
- Add an algaecide as a preventative measure every three to five days. Pour the dose according to instructions into your pool skimmer, and let it sit for about twenty-four hours. You can then vacuum your pool to get rid of any dead algae that may have gathered at the bottom.
In Conclusion
While these steps can help you get rid of algae that may be making your pool water cloudy, remember that prevention is always better than cure. Balancing the pH, performing regular shock treatments, and skimming debris from the surface are just a few tasks pool owners can do to keep their pool clean and clear all year round.
For more helpful pool information, check out our posts on whether cloudy pool water can be dangerous and if pollen can lead to cloudiness!
Hi, I’m Matt Harper, the founder of poolcareguy.com, a site I started with one simple mission: to help people around the world clean and take care of their pools and hot tubs on their own, without the hassle.
I’m not a professional pool cleaner and don’t have any formal training, I’m just an average guy who loves hanging out by his pool and hot tub and taking care of it. After many years on the job, I’ve become quite good at it.
On this website I will be teaching you absolutely everything I know about pools and hot tubs.
