Why your pool turns green and cloudy

While the rain doesn’t generally harm your pool, it can dilute the carefully balanced chemistry in the water. This can alter your pH levels and dilute the chlorine or other sanitizers, allowing algae or other contaminants to gain a foothold. Once the algae spores have the proper conditions to grow, they multiply very quickly, which is why your pool can turn green overnight. A pool full of algae isn’t just unsightly – it presents potential health problems for swimmers in the form of skin irritation, ear and eye infections, and gastrointestinal illness. It’s also possible for run-off from the storm to bring unwanted chemicals like nitrates and phosphates into the pool, further clouding the water.

Prevent dilution before it occurs

The best way to keep your pool water clear is to prevent rainwater from diluting it in the first place. Keep an eye on the weather forecast during the swimming season and pull the pool cover in place before any storms settle in over your region. A good quality pool cover is a worthy investment, as cheaper models made with lightweight plastic vinyl are more likely to tear over time and allow the rain to infiltrate the pool. If you don’t have a pool cover, you can get a head start on cleanup by adding algaecide to the water and sweeping away any debris near the pool before the rain arrives.

Clean debris from the pool

If you missed your opportunity to cover the pool and are left with cloudy, green pool water, all isn’t lost. With a small amount of remediation work, you’ll be happily swimming again in no time. The first step is to remove any leaves, twigs or branches that found their way into the water.  Also, check the filters and the pump and skimmer baskets to ensure they aren’t clogged. In addition, you’ll want to brush off foreign objects that have lodged themselves on the ladder or steps and then vacuum up any debris that has settled on the bottom of the pool.

Make sure your water level is correct

Many pools automatically drain excess water on their own, but if yours does not, you’ll need to remove some water to get back to the proper level before you start rebalancing the chemicals. You can open the drain, backwash the sand filter, or follow whatever the proper procedure is for your installation to get the water back down to around the center of the skimmer float.

Test the Pool Water

Once you verify that you have the correct amount of water in your pool, it’s time to check the pH, total alkalinity, and calcium hardness levels so you know if the water is swimmable. Heavy rains dilute the chemicals and may carry particulate matter from the air, which can raise or lower your pool’s pH level. When it comes to free chlorine, it’s a good idea to add a little extra, especially if there were leaves or other organic debris in the water. Typically, your pool should fall within the following ranges, but check your manual for specific instructions for your setup:

• Total Alkalinity: 100-150 ppm. Works as a shock absorber to prevent spiking pH levels.
• pH: 7.2 – 7.6 Too low causes irritation. Too high causes calcium scaling.
• Calcium Hardness: 180-220 ppm. A neutral level helps preserve concrete or plaster-lined pools.

Run the Pump and Filter the Water

Verify that the water is able to properly complete its journey through all the circulatory equipment and that the filter pressure is at normal levels. Once you’ve achieved good circulation and filtration, let the system run before you give the pool a test swim. The amount of time the equipment will take to totally clear the water will vary depending on what type of filter you use – anywhere from a few hours if the filter uses diatomaceous earth to several days for a sand filter. As a general principle, change out paper cartridge pump filters regularly. You can make these filters last longer by washing them out with a hose and soaking them overnight in a bucket of white vinegar or bleach. If you use a sand filter system, be sure to perform a back flush according to the manufacturer’s recommendations.

Give the Pool a Shock

If the pool is still very cloudy or green, you may need to shock it to make it safe to swim in again.

1. First, make sure that the filter system is working properly, and the chemicals are still at the proper levels.
2. Next, mix up your chlorine shock (hyperchlorinate) treatment. Add 1 pound of your preferred shock treatment into a 5-gallon bucket of water about 3/4 full (the exact measurements may vary depending on the size of your pool and how contaminated the water is).
3. Slowly pour this mixture directly into the pool water. Do NOT add shock directly to the skimmer, as undiluted, full-strength pool chemicals can damage filters, heaters, and pumps.

Maintain the higher shock levels to kill off all the algae. This can take several days and involve multiple treatments to get combined Chloramines and FC levels to the right levels that clear the water. While performing the treatment, brush and clean the pool thoroughly every day to remove dead algae and other dirt.

More pool cleaning tips

• Chlorine becomes stabilized or un-stabilized. Stabilized chlorine is coated with Cyanuric acid to prevent Cl2 from evaporating. Un-stabilized chlorine, such as sodium hypochlorite, is not treated with Cyanuric acid.
• Sodium hypochlorite, also known as pool bleach, is available as a liquid and is highly concentrated compared to household bleach. Calcium hypochlorite is available as a granular powder or slow-release tablets. Both of these chemicals are used to shock the pool to raise the concentration of free chlorine (FC) in the water.
• Calcium hypochlorite reacts vigorously with water to release free chlorine — but it dissolves slowly. To get the freest chlorine into the water, add it to your pool at night so it won’t evaporate as quickly. You’ll need to wait 8 hours to use the pool, anyway. Calcium acts as an alkaline buffer.

When in doubt, consult the instructions that came with your pool, or schedule an appointment with a professional to resolve any questions and ensure that your pool provides a clean, safe and relaxing environment for you and your family.