High sunlight and high temperatures mean that biofilm in our pool develops at an express rate. The effect can be seen and felt. The water ceases to be transparent and becomes green. This is a common problem that can be easily combated. Most importantly, it is not necessary to replace all the water in the tank.

  • Green water is caused by several factors
  • The problem can be rectified by shock chlorination
  • Using professional chemistry reduces the likelihood of recurrence of the problem

Causes of green water in the pool

A. Poorly selected pool filter

This problem applies mainly to supermarket pools. The manufacturer of these pools supplies cartridge filters or paper derivatives, uniform for all capacities of pools of this type.

Unfortunately, filtration based on this type of "invention" is inefficient and has no right to function properly. In the first instance, if you own a pool of this type, you should invest in a small sand filter and an appropriately sized filtration pump. Such a filter set is selected according to the capacity and size of the pool (measured in m3).

B. Filter cycle too short

This is usually due to the apparent saving of electricity by the User. Filtration should operate a minimum of 8 hours a day. As a rule of thumb, for private pools, we recommend that it should operate from 8 a.m. to 8 p.m. Bear in mind that a small energy saving will result in the need to purchase additional pool chemicals and will probably put the pool out of service for several days.

C. Poorly chosen filtration times

Filtracja powinna działała wtedy kiedy korzystamy z basenu, zwyczajowo jest to dzień. Filtracja musi być trwała, systematyczna i odbywać się wtedy kiedy basen jest użytkowany, ponieważ:

użytkując basen wspomagamy obieg wody wewnątrz niecki basenowej, co wspomaga odpowiednią filtrację

korzystając z basenu zanieczyszczamy go, a włączona filtracja na bieżąco oczyszcza wodę, dzięki czemu ograniczymy rozwój mikroorganizmów

w dzień basen narażony jest na wpływ warunków atmosferycznych (nasłonecznienie, temperatura), które sprzyjają rozwojowi grzybów, bakterii czy glonów, w szczególności w wodzie „stojącej”. 

D. Non-systematic flushing of the pool filter

This is a point that most users do not remember or do not know about. It is essential to rinse the filter regularly. In the case of systematic use of the pool, even once a week.

Every professional filter set is equipped with a 6- or 4-way valve, with the help of which we rinse the pool filter.

The whole procedure for rinsing the pool filter should not take longer than 10 minutes, and this is extremely important for the quality of the pool water.

E. Unsystematic use of pool chemistry

On every pack of chemistry we supply, there is a precise description of how and how much chemistry should be applied per m3 of water. In the case of manual dosing, special care must be taken to ensure that the chemistry is present in the water at all times. We recommend the use of multi-purpose tablets and dosing buoys.

F. Low-quality swimming pool chemicals

This is the root cause of pool water maintenance problems. Only the use of high-quality, reputable chemicals will keep the pool water in good condition. It's not about the quantity of chemicals used but about their quality and performance. Cheap pool chemicals are made from chemical waste, which, apart from being poorly effective, affects the health of the user. We recommend using products from European manufacturers - HTH (France), Bayrol (Germany) or Chemoform (Germany) - whose quality is incomparable to cheap market equivalents.

Can you bathe in green water and is it harmful?

Green water in a swimming pool is a sign that bacteria, fungi, pathogens and parasites are developing and are a danger to the health of users. Incorrect water parameters rule out the possibility of using the pool and bathing in complete safety.

Only with proper filtration and maintenance of the correct amount of chemicals in the pool water is safety guaranteed. That is why it is so important to maintain the correct ph of the water, to measure the parameters regularly (using hand-held or electronic testers) and to use professional pool chemicals appropriately selected and adapted to your pool. 

Action procedure - green pool water - step by step

Thoroughly rinse your pool filter:

This point is quite often forgotten by customers, and undoubtedly regular rinsing of the filter, is a guarantee of keeping the bed in good condition and of optimal water flow through the pool filter.

With moderate use of the pool, the filter should be flushed once every 14 days, while with increased occupancy it should be flushed once every 7 days.

1. Switch off the filter pump in the electrical cabinet ("0" position).
2. Turn the 6-way valve to position 2 "rinse"
3. Switch on the filter pump on the electrical cabinet (position "R") for a time of approx. 2-3min.
4. After 2-3min, switch off the pump and turn the valve handle to position 3 "laying".
5. Switch on the filter pump on the electrical cabinet (position "R") for a time of approx. 15-30 sec.
6. After 15-30 seconds, switch off the pump and turn the valve handle to position 1 "filtration".
7. Switch on the filter pump on the electrical cabinet (position "Z").

The filter has been flushed out.

Check the pH of your pool water using a suitable tester:

There are currently 3 measurement methods on the market for which you can use:

    1. Tablet hand tester
    2. Strip hand tester
    3. Electric photometer

Adjust the pH to the correct level:

Depending on the readings you obtained when measuring the water with the tester, you must now bring the pH of the pool water to a level of 7.0 - 7.4. It is in this range that the chlorine will work optimally obtaining its maximum chemical effectiveness.

Of course, to lower the pH of the water, use pH Minus and to raise the pH of the water, use pH Plus accordingly.

Carry out shock chlorination - use shock chlorine:

This procedure is nothing more than a sudden increase in the chlorine content of the water, thanks to which we will eliminate all the micro-organisms that are present in the pool.

So-called 'chlorination' is another way of saying a breaking point, which will give you the effect of crystal-clear pool water.

Procedure (with filtration on)

1. Dissolve an appropriate dose of shock chlorine in warm water in a bucket and spread along the pool edge line.
2. Alternatively, dispense granules directly into the skimmer.
3. Leave filtration on for min. 48 hours
4. After approx. 24 hours, test the pool water with a suitable tester or photometer.
5. Do not use the pool until the target chlorine content of the water is close to 0.6 mg/l.
6. After 48 hours, rinse out the pool filter again and start disinfection with the multifunctional, long-soluble tablets.

Apply coagulant in the form of cartridges:

Along with the application of the shock chlorination discussed earlier, include a flocculant in cartridges in the operation as well - this will aid the crystallisation of the water and cause the dirt to clump together in so-called 'clusters' - in other words, it will improve the filtration process.

Note: After the coagulant has been applied, the pool filter will (plan) become dirty more quickly and will need to be rinsed out more quickly.

Mechanically remove the debris - using a manual or automatic vacuum cleaner

If you want to be fully effective, don't forget to remove the residue mechanically - with a manual or automatic hoover.

By carrying out each of the points listed above, you will cause some of the algae, dirt or sediment to sink to the bottom of the pool and require manual or automatic removal. For heavy soiling, a repeat of the vacuuming procedure will be required.

Useful products

What can be done to prevent the green water situation from recurring

After shock disinfection, it is important to ensure that the situation with green water in the pool does not recur; to this end, it is advisable to purchase chemicals from top European manufacturers and carry out the following steps:

pH readjustment

In order to check the pH level of the pool water, the pool water should be measured with a special tester. The pH of the pool water should be maintained at a level of 7.0 - 7.4. Suitable testers are used for this purpose.

Use of multifunctional tablets

These are chlorine tablets, long-soluble, in the form of 200g or 20g discs. They contain chlorine, a pH regulator, an algicide and a crystalliser. The systematic use of this product guarantees us crystal-clear water with a minimum of effort and attention.

The principle of use is simple - throw the appropriate number of tablets (according to the instructions) into the skimmer or dosing buoy, and after they dissolve, replace them with new tablets. With regular use, 1 tablet should be sufficient for approx. 2 weeks.

Flocculant in cartridges

Simultaneous use, as with shock disinfection, will make it easier to filter and vacuum the pool and keep the water crystal clear.


W przypadku basenów bardzo nasłonecznionych, zalecamy aby prewencyjnie (raz w tygodniu) stosować środek do walki z glonami.


- the pH of the water must be maintained at between 7.0 and 7.4
- the filtration must operate min. 8 hours per day - Flush the filter regularly
- do not forget to dose chlorine tablets
- do not use the pool immediately after shock chlorination

Zobacz wszystkie produkty w kategorii antyglon do basenu

Expert Advice!

Expected effect

It is possible that by following our recommendations, the first changes in the appearance of the pool water will be visible after just a short while, but some of the actions described above require a staggered process and all of this is determined by the capacity of your pool, which significantly affects the speed of activation of the desired chemical reactions.

It should be assumed that the full effect of your work will be visible after approx. 48 hours (assuming continuous filtration).

Day 1

  1. Start of filtration for min. 48 hours   
  2. Rinsing of the pool filter   
  3. Reduction of the water pH to 7.0 - 7.4   
  4. Injection of chlorine shock and flocculant

Day 2

  1.  Measuring the pool water parameters
  2. Vacuuming the bottom of the pool

Day 3

  1. Rinsing the pool filter   
  2. Achieving a chlorine content of 0.6 mg/l in the water   
  3. Beginning of continuous disinfection with multi-purpose tablets   
  4. Vacuuming the bottom if necessary

Home remedies for green pool water

·  Green water and vitamin C

·  Green water and ascorbic acid

·  Green water and citric acid

In your search for answers to the question of green water in swimming pools, you may have come across the above queries, suggesting that the use of vitamin C or its derivatives has a positive effect on solving the problem.

Nothing could be further from the truth!

As such a theory is encountered in the world of the internet, we have decided to deal with this thread once and for all, dedicating a separate article to this issue.


Green pool water after rainfall

Heavy rain affects the pH of the pool water significantly lowering it, which has a direct impact on optimal disinfection. The pool water should have a pH level of 7.0 - 7.4.

Check the chlorine level in the pool water, which is probably too low.

Green water in the garden pool

A change in the colour of the water in a garden pool is usually a rapid spread of algae. This phenomenon will increase on warm, sunny days. The first symptom of algae in the pool will be slippery walls and bottom.

There may be several causes, including

    inefficient or no filtration
    a pool filter that has not been rinsed out
    lack of constant water disinfection with dedicated pool chemicals

You should:

    adjust the pH of the water
    shock disinfection
    use coagulant
    Vacuum the pool

Green pool water after addition of chlorine

This phenomenon, is the result of too much iron in the pool water. In the vast majority of cases, this problem occurs in users who have poured water from a well into the pool rather than from the water supply.

Well water, by custom, is rich in various chemical and organic compounds. We recommend that the water for the pool is poured from the mains water supply (which, unfortunately, is also not 100% reliable as some mains water systems have a low de-gelatinisation capacity).

When chlorine is added to the pool, with water with a high iron content, a chemical reaction (oxidation of the iron) takes place, resulting in the precipitation of a green-brown colour in the water, which settles in the pool basin and can become difficult to remove over time.

Of course, getting rid of the iron is possible, all you need to do is:

- have efficient filtration (with a washed out sand filter)

- adjust the pH

- carry out shock chlorination

- inject coagulant

- inject Metal Magic

During the above-mentioned period, the filtration should operate for at least 48h.

It is necessary to check the pool filter for contamination and to rinse it again. Some of the dirt will settle on the bottom and should be vacuumed out using a hand or automatic hoover.

Green water in the pool immediately after pouring

The usual colour is green-brown and this is due to high levels of iron in the water.

We recommend that you pour water into your pool from the water supply and not, for example, from a well in your garden.

This is not always possible, so the pH of the water must be adjusted, shock chlorination must be carried out, coagulant and Metal Magic must be dosed. Of course, the pool filtration must be running at all times.

Green bottom in the pool

The green bottom in the pool is the result of algae and algal growth. The problem lies with the filtration capacity and too little chlorine in the pool.

The pool water parameters should be tested, the pH adjusted and shock chlorination carried out. After about 24 hours, vacuum the pool and rinse out the filter.

What to do with green pool water?

A full shock chlorination procedure should be carried out, along with vacuuming the pool and rinsing the pool filter.

Only continuous, controlled disinfection will avoid the growth of micro-organisms in the pool water.

FAQ - Questions and answers

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Team Poolsystem.pl
Tomasz Tomkowicz

Pool Technology Specialist

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