We speak to many customers who ask how to remove green algae from their swimming pool. It’s a situation that no pool owner wants to be in, but the good news is that with proper pool water care, algae problems are almost completely preventable. But when green algae appear in your pool, it can quickly become your worst nightmare. It takes time, money, and a good deal of effort to remove it. In addition, because the algae are already present, your water may now also be contaminated with pathogens, bacteria, and other unwanted elements. Swimming in this water could cause irritation to your eyes, skin, and any open cuts you may have, so using your pool is now out of the question. Green algae play an important part in the natural ecosystem, supporting food chains both in the water and on land, as well as helping to produce the air we breathe. However, when they grow in our pool, they don’t come as friends.

What Causes Green Algae to Grow in a Pool?

Heat, direct sunlight, CO2, and a few naturally formed nutrients cause algae to develop nearly anywhere in the outdoors. Your pool water is also vulnerable due to use by swimmers, thus making the problem more common during the midsummer months than at any other time of year. Another cause of algae in your pool is from not using algaecide before the problem occurs. Many people believe that they need to buy an algaecide to get rid of the algae but in fact, algaecides are best used as a preventative measure. In other words, if you already have green algae in your pool, it’s too late for algaecide and you’ll need to take several other steps to make your water enjoyable again. 

How to Get Rid of Green Algae

Once you find green algae in your pool, you must kill it by shocking your pool water with high levels of chlorine. If the algae problem is extremely bad, you’ll have to take stronger measures to eliminate it completely:

1. For a bad algae situation, start by turning your vacuum to “waste” (for sand filters only), which will take the water and the algae directly out of your pool. Set your filter back to “filtration” when finished.
2. Vacuum up as much of the algae as possible and clean your pool filter.
3. Test your pool water’s pH level, as algae thrives in a high pH environment. In most cases, lots of algae will create a high pH level, so if the pH level is higher than 7.6 add a reducer to your pool water to bring the level down. This will make a less desirable environment for algae and will make your shock in the step 5 more effective.
4. Keep the pump operating continuously for a few hours to let the pH reducer to evenly disperse before proceeding.
5. Shock the pool with a large dose of chlorine, such as Burn-Out^® or BioGuard^® Power Chlor^®. You want the chlorine to be at about 10 ppm or higher which requires you to add more shock product than you normally would. Remember that this is best done at the end of the day so your chlorine is not impacted by direct sunlight.
6. 20 – 30 minutes after shocking, brush the whole pool down, including the walls and floor, to dislodge the algae from these surfaces where algae are protected. This will expose the algae to the high amount of chlorine you added, increasing the chances of killing it quickly.
7. If the pool is still green the following day, shock the pool water again, and repeat brushing if algae still exist on the walls or floor of your pool.

By following these steps, you should see the pool water change overnight from green to cloudy or murky as the algae dies. Once the water turns cloudy, backwash or clean your filter and maintain chlorine levels at around 3ppm. You can also start using a clarifier such as BioGuard Clarifying Tabs^®.  Because algae particles are smaller than what your filter can capture, these tabs will help clear your pool up quicker than by just using a filter alone. It’s important not to swim in the pool once you start this process and until your water is tested and deemed safe to swim in. The high level of chlorine needed to kill algae is not recommended for human eyes and skin to be exposed to. If you’re unsure about the safety of your water, bring a clean 500 ml sample of your water to our store at 309 Lakeshore Road East in Mississauga for a free water test. In five minutes, you’ll have the printed results and our recommendations on how to keep your pool water safe and always ready to use.

Which Chemicals Stop Algae from Forming?

Depending on the type of algae that had appeared in your pool, treatment may take several days or longer to completely solve the problem. But once gone, it’s relatively easy to keep your pool clean for the rest of the season. To prevent algae from forming again, we recommend you use an algaecide such as BioGuard Banish^® on a weekly basis. After applying the algaecide, it’s best to wait about 30 minutes before swimming again to allow the chemical to evenly disperse in the pool water. All of the pool watercare products we carry at Lakeshore Pools & Hot Tubs offer a safe, easy way to keep your pool water clean, clear, and swim ready all season long. The trick is to know how to balance them, how often to use them, and to know which ones best suit your particular needs. Visit our store to speak to our award-winning service team if you need any help. Algae can live in the swamp, not in your pool! If you’re experiencing algae, or have any other problems or questions about your pool water, contact our store at 905-891-8818, or visit us at 309 Lakeshore Road East in Mississauga. We’ll make sure you have a complete understanding of how to care for your pool water so you have a great swimming season!