"Heavy rain dilutes pool chemicals, especially salt and chlorine, which causes the pool to turn green. This means the water is not sanitised or healthy, so it's vital to address this.
Green Pool
With heavy rainfall, the chemicals in your pool can become unbalanced; your pH levels altered and your chlorine, salt and mineral content diluted. In addition, leaves, dirt and algae spores get delivered into your pool water and can decompose, causing phosphates to be deposited into your water.
Rainwater itself does not cause algae, but it can provide the right environment for algae. Rain will bring phosphates, nitrates and other organic contaminants into the pool. As we discussed earlier, rain also reduces chlorine levels.
The free chlorine levels might be low.
But be careful—adding too much chlorine in pool water can cause those metals to oxidize and turn the pool a different shade of green.
Test and Balance Water
Low Free Chlorine can cause your pool water to turn green. Always maintain Free Chlorine between 1 -4 ppm. If needed, apply the appropriate chlorine and sanitizers to restore adequate sanitizer levels.
While the green algae aren't harmful, the bacteria that feed on the algae can cause issues. When you swim in green water, you expose yourself to algae that host bacteria. Swimming in green water could cause bacterial infections on your skin, and you could get sick if you ingest algae-filled pool water.
A pool turns green when there is algae in the water. There are several reasons why algae could grow, but it is most commonly caused by prolonged exposure to the sun, rain and temperature spikes. These factors affect the chemical balance of the pool and result in the pool turning cloudy and/or green.
You need to raise the level of your chlorine – shock the pool – and maintain that high level until all the algae is dead. This may take 3 to 4 days.
If your pool is green but chlorine is high, it's possible that you aren't running the pool's filter often enough or for long enough to filter out algae and bacteria. In spring and summer, when it's warm outside, pools should be filtered for eight hours a day, regardless of whether the pool is in active use.
Baking Soda and Green, Blue, or Yellow Algae
You'll need to use an algaecide to kill the algae and superchlorinate your pool to clear the water. After this treatment, test your pH and alkalinity and add baking soda to raise alkalinity to at least 100 ppm and pH to between 7.2 and 7.8.
Low flow = poor circulation which will lead to algae in the pool. Bottom line, the filter must be backwashed on a regular basis to ensure that your pool water is clear. "When do we need to backwash?" - It is recommended to backwash your filter once every 4-6 weeks of regular use.
Pools can immediately turn green after shocking when they have metals like copper in the water. These metals oxidise when exposed to high levels of chlorine which makes the pool water turn green. Adding a metal control product such as Zodiac Metal Remover will help to restore the pool water.
After the hose fills with water, backwash your sand filter for 2 - 3 minutes, or until water runs clear.
It is not recommended to drain a swimming pool through the backwash valve. While sucking from the main drain and putting the water down the backwash line will work in some scenarios it puts your pool pump at risk of losing prime and running dry.
Put your hand over the inlet (where the basket is located on the side of the pool, not the pump) to feel if there's enough suction. Your hand should be sucked up against the inlet fairly quickly if the pump is set to its highest mode. If it's barely pulling, you likely have a clogged filter or a leak in the line.
Although, if you overdo the shock treatment, you risk getting green hair from chlorine due to the excess chlorine oxidizing the copper in the water. You can execute a shock treatment with a few different types of pool shock, just be mindful of how much you're using.
Just like you run vinegar through your coffee pot to get rid of calcium buildup, white vinegar can wipe away this eyesore in your pool. Mix a 50/50 solution of vinegar and water, dip a sponge or soft cloth into it, and scrub that residue away.
Clorox itself recommends using between 100 and 200 ounces of regular-strength bleach per 10,000 gallons of pool water -- one gallon is 128 ounces, and many bottles of bleach are available in one-gallon or half-gallon sizes. Pool professionals tend to recommend more conservative amounts of bleach.
It is important to know what exactly bleach is before you put it in your pool. Household bleach, Clorox and liquid chlorine can all be used to sanitize a pool. They are all types of chlorine. Household bleaches such as Clorox usually contain about 5-6% available chlorine, about half that of pool liquid chlorine.