Your Pool Went from Clean to Green Overnight. What Can You Do?

Your Pool Went from Clean to Green Overnight. What Can You Do?

Learn more about pHin, the Smart Water Care solution for pools and hot tubs.

You regularly test the water for proper chemical balance. You perform regular maintenance. You expect your pool water to sparkle like the ocean in the Caribbean; normally, it does. When you went to bed last night, everything looked fine, but when you got home from work today, you saw a foggy, green mess. What happened? Pools can't really turn green overnight, can they?

Yes, they can. It isn't the norm, of course, especially for a pool receiving regular maintenance. Under the right conditions, though (or should we say wrong conditions?) your pool can go from clean to green overnight. How does it happen? How can you fix it? And, how do you guard against it happening again? Read on!

Algae: The Green Monster

Algae grow fast. The human eye is typically blind to this microscopic plant life, unable to detect the little monsters until their level reaches somewhere in the vicinity of 30 million spores to an ounce of water!

Typically, a balanced pH and sanitizer level help keep algae at bay and pool water sparkling. Occasionally though, unusual conditions align perfectly to throw the whole thing out of whack. The result is murky, cloudy, green pool water. What's the biggest culprit? Wind blowing the airborne algae spores along with organic waste like leaves, dust, perspiration, body oils, etc. being introduced to the pool.

Technically, wind doesn't turn your pool green. Wind is like the getaway driver; he doesn't actually perform the heist, he just gets all the bad guys to the bank. Gusting or sustained winds work the same way, ushering dirt, debris, dead leaves, and more into your pool. A lot of that stuff contains minerals that algae thrive on, while also blocking your sanitizers so they don't work properly. Throw in an extra-warm day and you have the perfect conditions for green water.

Humans wreak the same havoc. If you recently entertained people in your pool, sweat, sunscreen, and other contaminants give algae just the boost it needs for a growth spurt. That's why we recommend testing and balancing the water a few days before your party, and then performing a shock treatment within 24 hours of the last guest leaving.

Algae spores can also hitch a ride on your swimsuit or towel and infest the next pool or hot tub you swim or soak in. Yes, some algae strains can actually come out of water, dry, and when introduced to the next body of water begin a new existence.

Shock It!

If you're looking at cloudy, green water, a series of shock treatments should clear it up within a day or two. However, you must attack the algae that first day, and then check the chlorine levels every hour. If you do not have test strips that measure chlorine concentration, head to the pool store.

Your first step is using your pool brush to scrub the walls and floor. This breaks up the algae, allowing the chemicals to work quicker. For a simple light green algae, adjust the pH to within the acceptable range, then perform a double shock treatment dose of 2 lbs per 10,000 gallons of pool water. A medium to dark green gets a triple dose of 3 lbs per 10,000 gallons. If you're looking at dark, blackish green water, you may need to do a quadruple shot. In general, if you maintain your pool regularly and this happens overnight, a double dose should be enough.

Leave the brush in the pool or hot tub during the treatment process to assure you are destroying as much of the algae as possible.

For best results, either use a liquid treatment or pre-dissolve a granular shock treatment. Avoid pouring water onto the chemical when dissolving granules in a basin or pail. Instead, add the granules to water and gently blend to dissolve. Slowly pour the treatment into the pool, evenly distributing it. Running the filter helps to mix and distribute the shock treatment.

Check the chlorine concentration every hour. You want shock levels of chlorine for this entire first day. If levels drop too low, complete another shock treatment. Your water should return to normal by the following day. If so, perform a full cleaning, including netting, sweeping, vacuuming, cleaning the filters, and re-balancing the water chemicals.

If you're still looking at green water, it may be time to call a professional pool tech.


There are two types of algaecide treatments: quaternary ammonia and metallic. Quaternary ammonia is cheaper and does not stain swimming pools, making it the more popular choice despite its foaming properties. Metallic algaecides, made from silver and copper, may stain some components.

Choose algaecides with an active ingredient (either ammonia or metal) of at least 30 percent. Concentrations lower than 30 percent may not kill the algae. Let the algaecide sit for 24 hours before performing any other maintenance.

Double-team the Green

Combining algaecide and shock treatments is the most effective way to eradicate algae. Go in alphabetical order, meaning algaecide and then shock, for the best results.

Once you kill the algae, get it out of the pool with your vacuum. If using the filter, make sure it is set to waste. Thoroughly clean filters to ensure algae don't begin to bloom again. Finally, test and rebalance the water.

Perform Regular Maintenance

In addition to creating the perfect environment for algae, poorly maintained pools present potential health risks. Swimming in a dirty pool leads to a variety of illnesses, including infections of the skin, eyes, ears, and digestive tract. Pool owners also face potentially pricey repairs. Like a car, maintenance is cheaper than repairs.

Luckily, maintaining proper chemical balance is a breeze with a pHin smart monitor. pHin monitors water quality 24/7, notifies you when it’s time to add chemicals, and ships you exactly what you need, in pre-measured doses. Just drop in the color-coded pod and enjoy clean, perfectly balanced pool water all season long.

Latest Posts

Load more posts