The green water in the pool is often due to the presence of algae in the pool. Algae blooms can appear when your pool has a low level of free chlorine. Exposure to high temperatures, heavy rains or poor circulation, without the use of a preventive algaecide, also increases the risk of developing pool algae. Algae growth turns the pool green and algae grow when the pool water lacks chlorine.
Why is my pool green? Green discoloration is a reaction to algae growing in the pool; it can grow and spread rapidly, especially in hot climates. In fact, on a particularly hot day, a mild case can turn into an algae infection during the night. It is very likely that algae have grown and spread due to an imbalance of chlorine in the water. The first and most common reason pool water turns green is a lack of chlorine.
Without chlorine in the water, the pool will start growing algae quickly. If chlorine is not added to the water once this process starts, algae can grow to a point where the entire pool turns green in a day. The hotter the water, the faster this process will be. Do you have a green pool? It won't be fun to swim or watch.
You don't have to empty your pool and start over. You can kill algae in the pool quickly and prevent them from coming back. Pool clarifier binds particles together so that they are large enough for the filter to grasp. If you have algae, it's impossible for the filter to remove all of them.
Instead, you must kill it with chlorine. You can physically remove algae by using pool flocs, which sink algae to the bottom of the pool, but requires a lot of work to vacuum them up. Read our full guide to algae for swimming pools here. Algae make the pool green and a chemical imbalance allows algae to grow.
If there is enough free chlorine in the pool, algae will struggle to form. If for some reason chlorine cannot accumulate at a high enough level, algae will grow. That's why you apply chlorine to your pool as part of the six-step process below. If green reappears, you can adjust the levels of chemicals other than chlorine, as there is more to pool water chemistry than chlorine alone.
Algae are a simple plant, which grows in water that offers them food and a hospitable (welcoming) environment. It doesn't take much for algae to enter your pool. Algae can be transmitted through the air or enter the pool on debris, a bathing suit, or a pool toy. When you find water with nitrogen and phosphorus, which is not protected, algae begin to eat and bloom can appear overnight.
Disinfectant makes your pool inhospitable to algae and kills it. If you don't test often enough and don't add enough bromine or chlorine (or any type of disinfectant you use), you're at high risk of contracting algae in your pool. Mother Nature rarely fits our schedules, and her testing regimen is another one she'll ignore. Many things make it more likely that your pool will need additional testing, as they increase the likelihood of algae blooming.
If any of these things happen in your area or in your pool, you're more likely to face algae bloom and you'll want to get tested more often. Daily or every other day isn't going to be too much. It's time to hit your pool, and by shock we mean superchlorinate. You'll add a lot of chlorine.
Even if you normally use a different disinfectant to remove algae, you must fight dirt. Hitting your pool eliminates exactly zero algae. What it does is kill it, so you can let the filter clean it. No matter what type of filter you use, whether it's a cartridge, sand or diatomaceous earth (DE), you'll need to clean it several times while cleaning the water.
You can also consider adding a few things here to help in the process. An algaecide, which also kills algae, and a flocculant (causes dead algae to accumulate to facilitate filtration) are added after a couple of hours of chlorine circulation. You can also wait until you're pretty sure you have them all, to be sure. At this point, the extra steps may not be worth it.
However, if you still have any algae that you haven't seen, it could bloom again quite quickly. Finally, testing isn't beneficial if you don't also fix what needs to be fixed; keep the water balanced, the disinfectant optimized, and the filter clean and fit to control algae forever. Since pollen doesn't stick to the pool surface, you won't often see it on the sides of the pool, where algae are commonly found stuck to the walls and bottom of the pool. Since you've scrubbed and vacuumed your pool and tested the water balance, your pool damper is ready to do what it was created.
If the water is a darker shade of green, almost black, it has been left untreated for a long time and will require professional pool treatment. And when that happens, potentially harmful bacteria that your disinfectant is supposed to neutralize surround you and your loved ones in every bathroom. Although not necessary, this is a great idea if your pool has contracted more algae than just this time. Most pool water tests don't measure phosphate levels, so ask a pool and spa store to test them or buy test strips, such as the phosphate test kit from Ets Hach Company.
Be sure to use conveniently packed one pound bags so you know you are using the right amount for your pool. But be careful adding too much chlorine in the pool water can cause those metals to rust and the pool to take on a different shade of green. Keep the pH low (7.2 - 7), run the pump as often as possible, and clean the filter daily until the pool is clean. Despite the color, the water will still be quite clear and you should be able to see the bottom of the pool.
The simple, but annoying, reason for a green pool is usually due to a lack of sufficient water and disinfectant tests. Typically, you may not associate swimming pools with the color green, unless you've personally experienced what high chlorine can do to blonde hair and switched to a saltwater generator. If the pool turned green immediately after hitting the pool, then there is an imbalance with other chemicals or something else has been added to the water that shouldn't have. It may not operate the filter long enough to clean the water well in hot weather, the pool filter should work for 8 hours a day and, if there are a lot of people using it, possibly longer.