Why Do I Have a Green Pool?
When your pool water turns from a lovely shade of blue to a sickly green, there’s only one reason: pool algae. If it’s a light green, the algae has probably just started to take hold. But a deeper green means a bigger problem.
Algae develops when the pool’s sanitiser levels are too low. If you haven’t been keeping up with pool water testing and water balancing, or you’re not adding enough chlorine, bromine, or whatever type of sanitiser you use, you’re practically laying out the welcome mat for algae to come in and make itself at home.
How to Fix a Green Pool Fast
- Vacuum your pool to waste
Once you start removing algae and debris from your pool, you obviously don’t want anything you take out to make its way back in. So your first step is to vacuum the pool to Waste. Set the valve on your filter to Waste, then vacuum away, removing as much algae and sediment from the bottom of the pool as you can. Use your Hi-Vac Sweeper Brush to Vacuum your pool.
- Brush the pool walls and floor
Rather than just your usual, regular pool brush, it’s best to use an algae brush for this task. Algae is tough, and will stubbornly cling to the pool’s surfaces, so a heavy-duty brush works better than soft nylon bristles to remove it. Use the brush to scrub the pool walls, floor, steps, and any other surface the algae may be clinging to.
- Test the water for pH and alkalinity
Using test strips or a liquid test kit, test the pH and alkalinity levels. Note the levels as you’ll refer to them later.
If you want to, you can also note the chlorine (or another sanitiser) level. We’re willing to bet it’s going to be too low or even non-existent. If the sanitiser level was where it should be, you wouldn’t be dealing with algae. It also won’t matter once you get to the next step.
- Shock your pool with chlorine to kill algae
This is the main event in clearing a green pool—killing the algae. Pool shock contains a high level of chlorine that will kill the algae and sanitize the pool. For the best results, use a shock that contains at least 70% available chlorine, and shock the pool twice.
Important: Even if you normally use non-chlorine shock, you must use chlorine shock to kill algae.
If your pool is dark green, meaning you have a larger algae infestation, we recommend shocking the pool three times. And if the colour of your green pool is reminiscent of a dark, spooky swamp, shock it four times. Remember to shock your pool at dusk or night. If you shock during the day, the sun will eat up most of the chlorine before it has a chance to kill the algae. And put your cleaning equipment in the shallow end while you shock your pool so your tools will also be sanitized. Also, treat your pool with an Algaecide at this point.
- Run, Filter, Run!
Once you’ve shocked the pool as many times as you’re going to shock it and treated it with an Algaecide, turn the pool pump on, and don’t turn it off until the water is completely clear. Here’s where those five days or less come in. Be patient.
Again, you can use a pool clarifier if you want to clear it more quickly, but even if you do, be sure to run the filter for at least 24 hours to get the dead algae out of the water, and ensure the shock has fully dissipated.
- Test, Balance, and Test Again
When your green pool isn’t green anymore, test the water, this time not just for pH and alkalinity, but also for sanitiser. Add chemicals as needed to balance things out. Test it again to make sure everything’s as it should be, and you’re ready to enjoy your pool again.
A Little Pool Chemistry 101:
Why is PH important?
Three reasons. First, as pH goes up, the ability of free chlorine to kill germs decreases, especially if pH is >8.0. Second, as pH goes down, especially if pH is <7.0, the ability of free chlorine to kill germs increases but the pool or hot tub/spa pipes are more likely to corrode or break down. Third, keeping the pH in the 7.2–7.8 range helps keep swimmers comfortable in the water by helping to prevent eye and skin irritation. This means keeping the pH in the 7.2–7.8 range best balances killing germs to prevent recreational water illness, the lifespan of the pipes, and swimmers’ comfort.
What does chlorine do?
Chlorine is added to the water to kill germs. But it does not work right away. If used properly, free chlorine* can kill most germs within a few minutes. CDC recommends pH 7.2–7.8 and a free chlorine concentration of at least 1 ppm in pools and at least 3 ppm in hot tubs/spas.
If using cyanuric acid, a chlorine stabilizer, or chlorine products with cyanuric acid (for example, products commonly known as dichlor or trichlor [see product label]), CDC recommends pH 7.2–7.8 and a free available chlorine concentration of at least 2 ppm in pools. CDC recommends not using cyanuric acid or chlorine products with cyanuric acid in hot tubs/spas.
* Free available chlorine is the more active form of chlorine that kills germs.
Why does chlorine need to be tested regularly?
All sorts of things can reduce chlorine concentration in pool or hot tub/spa water. Free available chlorine breaks down pee, poop, sweat, and dirt from swimmers’ bodies instead of killing germs and uses up chlorine, which means there is less to kill germs. The sunlight and hot tub/spa jets creating droplets or mists from the water also uses up free chlorine. That’s why the free chlorine concentration must be routinely tested. And remember, the time it takes for free chlorine to kill germs is also affected by the other member of the disinfection team, pH.
How do I test chlorine and pH levels in my pool?
For the everyday Joe who does not have time to do a whole chemistry course to test his/her pool, Aquachek Test Strips are quite sufficient. They test PH, Free Chlorine, Total Alkalinity and Stabilizer which are your most common indicators of a healthy pool. Ph must be between 7.2-7.8, Free chlorine between 1-3ppm, Total Alkalinity between 80-100ppm and Stabilizer between 50-100ppm. This is accomplished by dipping the test strip into the water for 10 seconds and reading the colour chart on the back of the bottle.
How often should I test chlorine and pH levels in my pool?
In your average pool where you are already treating your pool at least twice a week with Chlorine, it is not necessary to test your pool more than once a week.
How quickly does chlorine kill common illness-causing germs?
Free chlorine kills most bacteria, such as E. coli 0157:H7, in less than a minute if its concentration and pH are maintained as CDC recommends. However, a few germs are moderately (Giardia, Hepatitis A) to very (Cryptosporidium) chlorine tolerant. The table below shows the approximate times it takes for free chlorine to kill these germs.
Free Available Chlorine Germ-Killing Timetable
E. coli 0157:H7 (Bacterium) = Less than 1 minute
Hepatitis A (Virus) = Approximately 16 minutes
Giardia (Parasite) = Approximately 45 minutes
Cryptosporidium (Parasite) = Approximately 15,300 minutes (10.6 days)
Times based on 1 ppm free chlorine at pH 7.5 and 77°F (25°C)
These disinfection times are only for pools and hot tubs/spas that do not use cyanuric acid. Disinfection times are longer in the presence of cyanuric acid.