The best way how to clean a green pool

Clean a green pool

It is quite simple to get clean a green pool, and even simpler to prevent the appearance of the problem. We will see in detail why pool water turns green, and the best method to clean the water in less than 48 hours.

If there is yellow-ish area that seems like dirt or sand, it may be the mustard algae. See here how to get rid of the yellow algae in the pool.

Why does pool water turn green and cloudy?

Pool water turns green and cloudy when there is an algae bloom in the water. It is these algae that give the green color to the water.

Algae can appear very quickly, in less than 24 hours. You can leave for a weekend for a wedding and find the water green and full of algae on the way back.

Algae appear when water is poorly filtered or imbalanced. Most often it is:

  • a chlorine problem: for example not enough chlorine, too much pH, ​​too much stabilizer, not enough salt
  • a filtration problem: for example a clogged filter, a filter that is too old, or not enough filtration

We will determine the origin of the green water during the 2nd stage of the treatment, below.

Gradual appearance. A slippery, greasy surface is often the first sign that algae are appearing. We will then see some green spots per area, for example in the corners. The algae will then make themselves at home and invade the entire pool: the pool water will be green.

Clean a green pool in 3 steps

It is quite simple to clean a green pool in less than 48 hours. We will detail the operation in 3 steps:

  1. Clean the pool
  2. Restore water balance
  3. Do a super-chlorination

Too much seaweed? If you can’t see deeper than 25cm, there is too much seaweed. The water cannot be caught. You have to drain part of the basin and add clean water to be able to carry out the treatment.

1. Clean the pool

Remove large visible debris. The goal here is to catch as much trash as possible. This waste is usually treated by the pool skimmer or filter. We will use this equipment a lot afterward, it must be as efficient as possible, which is why we remove everything we can. You can use a landing net to catch all the debris or a pool vacuum. You have to go everywhere, on the surface, at the bottom, in the corners.

Scrub the walls. Some algae are well attached to the walls. By manually rubbing all the walls, the algae will come off. They will then be better treated by the chemicals and the filtration of the swimming pool. You can use a brush broom for this operation

2. Restore water balance

The water is known to be green because there has been an algae bloom. On the other hand, it is not yet known why the algae were able to develop so quickly. It is necessary to determine the probable cause of the appearance of algae to be able to eliminate it.

Test pool water. This is the first step in determining the origin of the problem. We will test the level of pH, disinfectant (Chlorine, Salt, Bromine), stabilizer, and salt for saltwater pools. Depending on the results:

  • pH too high: the higher the pH, the less effective the chlorine. The algae could then appear because the chlorine did not act enough. 6 ways to lower pool pH here.
  • pH too low: for bromine pools, the lower the pH, the less effective the bromine is, so it can be the cause of the appearance of algae. 6 ways to raise pool pH here.
  • Too little chlorine or bromine: Without a disinfectant like chlorine or bromine, algae can grow. If you have a salt pool, the chlorine that is too low may be due to a chlorine generator that does not produce enough, or that lacks salt. More information on pool chlorine here.
  • Stabilizer too high: the stabilizer blocks the action of chlorine. A pool that has too much stabilizer is like a pool without chlorine: the water turns green due to algae. More information on pool stabilizers here.

Check filtration. If you haven’t backwashed for a long time, it could have made the situation worse. You can therefore do a backwash now so that the filter regains its effectiveness. If the sand has not been replaced for 5 years, it will probably need to be replaced soon.

Having these checks, you should now have a fairly clear idea of ​​the causes that may have led to the appearance of algae in the pool, and green water. It is often several causes that combine.

Balance pool water. To be able to get rid of the algae, the water regains its normal state: a pH level of around 7.3, enough chlorine, and not too much stabilizer. We did not address the TAC, which has no connection with the green water of the swimming pool, but it must still be within the standards.

3. Shock the pool!

The swimming pool is ready to return to its normal state. The pool is cleaned, the water is balanced, and all that remains is to get rid of the algae residues that continue to float in the green water of the pool.

Chlorine Shock. The shock chlorine treatment will quickly kill all microorganisms, including algae. The operation consists of adding a large quantity of chlorine all at once, hence the name shock chlorine or super-chlorination. Chlorine is always quickly eliminated by the sun’s rays, UVs, so it does not create a problem over time. You can use quick dissolving chlorine shock tablets or liquid chlorine. Bleach is also possible, but much less effective because it is not very concentrated, you will have to use it a lot. See all products to increase chlorine in the pool here.

Filtration. The last operation is to filter the water. The shock chlorine has killed the algae, but there is still material in the water. To eliminate it, the pool water must be passed through the filter. The operation may take some time, let the filtration run for at least 8 hours.

Filtration directly follows the chlorine shock treatment. Filtration will make it possible to apply the action of shock chlorine in all the green water of the swimming pool, in a short time. The action time of the shock chlorine to treat the green water is therefore done at the same time as the filtration and lasts about 8 hours.

Once the water has been filtered, let’s conclude. If the pool water is still green despite the shock chlorine treatment, the treatment must be renewed. When there is a lot of algae, several chlorine shock treatments may be needed. It is not always possible to clean a green pool in less than 48 hours when there is a lot of algae. Also, check the water parameters to be sure the water is balanced.

Anti-algae to treat algae in the pool

The anti-algae, or algicide, is a preventive treatment. It is used to prevent the appearance of algae.

There is curative anti-algae, which helps destroy algae. It is used at the same time as chlorine shock. It is not essential, it helps when there is a lot of algae.

Never again

To protect yourself from the future appearance of algae in the pool, and from green water, the only solution is to regularly check the quality of the water and carry out daily maintenance. It is indeed tedious, and it takes time.


The water is green despite the pH and chlorine good, what to do?

Also check the other parameters we have mentioned, for example, the stabilizer or the sand filter.

How much chlorine shock can we do in series to clean a green pool?

When the pool has a lot of algae, it may need to do several treatments in a row. If the situation does not improve after 3 chlorine shock treatments, take a break and reassess the situation.

Despite the chlorine shock, my pool remains cloudy, what should I do?

When the pool remains cloudy after a chlorine shock to clean a green pool, it is certainly because the pool filter has not succeeded in eliminating everything. You can do backwashing of the filter so that it regains its efficiency, and restart the filtration for 8 hours. You can also use a clarifier or a flocculant, which will make it possible to form larger blocks of debris to be caught by the sand filter, or in the landing net.

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