Pool Chemicals 101: What, When, and How to Add Pool Chemicals

The pool chemistry is an essential part of pool cleaning so that the water stays clean. But what do you really need in a pool maintenance set, and which resources are just a waste of money?

The following chemicals are required for pool cleaning: Chlorine, a chlorine stabilizer, bromine, acids to raise or lower the pH level, a hardness stabilizer, algaecides against algae growth, and a flocculant for crystal clear water.

In this article, you will find out which pool chemicals you need to clean pool water and how these agents are used correctly in your pool.

Pool chemistry starter set: Instructions for a clean pool

Having your pool in the garden is easy to maintain once you get the hang of it.

Unlike many advisors who confuse new pool owners, pool maintenance is easy with understanding pool chemicals.

If you don’t have time to read the article, here is a list of the pool chemistry starter set:

  • Chlorine: For pool disinfection against organic substances.
  • Cyanuric acid: Serves as a chlorine stabilizer so that the chlorine works longer.
  • Bromine: The alternative to chlorine – but works weaker and slower.
  • pH plus and pH minus: To raise and lower the pH level.
  • Acid capacity: prevents large jumps in the pH level.
  • Calcium hardness: Important against cloudiness in the pool water.
  • Algaecide: Helps to inhibit the growth of algae in the swimming pool.
  • Flocculant: Binds fine particles and improves filtration.

Regular water tests are an essential requirement for optimizing the ideal level ​​in your pool – if necessary, use the water tester I recommended here.

Here you will find a table with the ideal level ​​for your swimming pool and how often these parameters should be measured per week.

Parameters Level Frequency of measurement
Chlorine 0,3 – 1,5 ppm 1-2x/Week
Cyanuric acid 30 – 50 ppm 1x/Month
Bromine 3,0 – 5,0 ppm 1-2x/Week
pH level 7,2 – 7,6 1-2x/Week
Alkalinity 80 – 120 ppm 1x/Month
Calcium 200 – 400 ppm 1x/Month

In the further article, I explain why the individual pool chemicals are necessary for pool cleaning and how they are used with the help of my instructions.

Reading tip: If you don’t understand something at the beginning or terms are unclear, just read on to the end. 

This article builds on each other with the individual headings, and I guarantee you that everything will make sense in the end.

Chlorine as a disinfectant in the pool

Because of its strong oxidizing power, chlorine is the most common method of disinfecting a pool and keeping it clean.

The use of chlorine is practical against:

  • Algae growth and cloudiness in the pool water.
  • Legionella and the legionnaire’s disease.
  • All kinds of germs and especially against E. Coli (Escherichia Coli).

Chlorine (CL) is a poisonous chemical, and therefore direct skin contact and the inhalation of the gases should be avoided.

But dissolved in the water and correctly dosed, the chlorine in your pool is harmless.

The chlorine is available as chlorine granulate, liquid chlorine, or chlorine tablets for the pool. A distinction is made between stabilized and non-stabilized chlorine.

The application is straightforward, but a few points should be observed before use so that the chlorine develops its full effect.

Depending on the consistency, the chlorine level in your pool can be corrected using a dosing system, a floater, or manually.

In the solid-state, chlorine is added with a dosing tank (floater) and not, as is often claimed, via the skimmer or pump.

It is best to hang the floater with a short line on the water flow of the return nozzles in your pool.

Admittedly, this sounds confusing to beginners, but you will learn to differentiate between chlorine and use it correctly.

To clarify the difference and the purposes of use, you will find a separate chapter for each chlorine variant in this article.

A stabilized chlorine for pool maintenance

Usually, stabilized chlorine (di-chlorine or tri-chlorine) is sold in pool shops.

This means that the chlorine products are stabilized from the rapid decomposition by the UV rays of the sun and heat.

  • Di-chlorine: The di-chlorine (sodium dichloroisocyanurate) is more soluble than the tri-chlorine.
  • Tri-chlorine: The tri-chlorine (trichloroisocyanuric acid) is an inexpensive alternative, and you need about 400 g per week in the high season – that’s about 10 to 12 kg per year.

Both variants are organic chlorine products and build up a high chlorine level in your pool due to the cyanuric acid they contain.

The di-chlorine and tri-chlorine are wonderfully suitable for ongoing disinfection of your pool water.

The chlorine granulate is also useful in combating local algae growth by applying the granulate to the infected areas.

I explain how to do this in the article on cleaning green pool water.

Unfortunately, the di-chlorine and tri-chlorine are unsuitable for a pool shock – also known as chlorine shock – because, as already mentioned, they are slowly broken down by the chlorine stabilizer (cyanuric acid) they contain.

Fast-acting chlorine products without a chlorine stabilizer are necessary for a pool shock. You can find out more in the following chapter.

Non-stabilized chlorine for pool maintenance

The non-stabilized chlorine does not contain cyanuric acid (chlorine stabilizer) and is usually sold as liquid chlorine.

But there are also liquid chlorine products that contain a chlorine stabilizer.

Since chlorine is easily broken down by the sun’s heat and UV rays and loses its effectiveness without a chlorine stabilizer, the liquid chlorine is wonderfully suitable for a pool shock in your swimming pool.

The liquid chlorine is available in different concentrations. Depending on the concentration, you need 5 to 10 liters of liquid chlorine per 25 m³ of water.

Wear protective goggles when using chlorine, as the splashes caused can damage your eyes – I also recommend wearing old clothes.

Tip: If necessary, non-stabilized chlorine can be used for permanent disinfection with an extra addition of cyanuric acid – I will go into this in more detail in the text.

The danger of chlorine by-products in the pool

When using chlorine, by-products such as chloramines and trihalomethanes develop in your pool.

  • Chloramines: The chloramines are formed when chlorine reacts with sweat and urea – the typical pool smell is a sign of a high proportion of chloramines (should not rise above 0.2 ppm)
  • Trihalomethanes: If the chlorine reacts with organic substances, trihalomethanes are formed – the concentration should remain below 2 ppm.

A regular water test can minimize the risk of illnesses and allergies from chlorine by-products.

An allergy to chlorine becomes noticeable with reddening of the skin, rashes, and runny nose.

On the other hand, Chloracne occurs when there is direct contact with chlorine. That is why you should always wear protective equipment when using chlorine.

Cyanuric Acid: Use a chlorine stabilizer

The term cyanuric acid was often used in the section about chlorine, and I briefly mentioned that this is a chlorine stabilizer.

If you use already stabilized chlorine granules (di-chlorine and tri-chlorine), you probably do not need to use cyanuric acid.

However, if you use non-stabilized chlorine and intend to use it to disinfect your pool in the long term, then a chlorine stabilizer must be added to the pool water.

The need for a chlorine stabilizer is based on the fact that non-stabilized chlorine, such as liquid chlorine, quickly breaks down under heat and UV rays from the sun and loses its effectiveness.

This means that you should use cyanuric acid in addition to the chlorine in your outdoor pool.

In contrast, you don’t need cyanuric acid in indoor pools or whirlpools.

The cyanuric acid protects the chlorine from decomposing quickly, but that’s not all.

With regular use of stabilized chlorine or with a separate addition of a chlorine stabilizer, the cyanuric acid level increases, which puts the effectiveness of chlorine at a disadvantage.

This means: From a cyanuric acid level above 50 ppm, the chlorine loses its effect and a water change is necessary because the cyanuric acid level doesn’t disappear by itself.

In my article, you can find more information about cyanuric acid and chlorine stabilizers. Just follow the link.

Bromine as an alternative to chlorine

Bromine is often used as an alternative to chlorine, but it is a highly poisonous pool chemical – direct skin contact should be avoided.

Again, I recommend wearing protective equipment for the eyes and respiratory tract.

Because of its weak oxidizing power, bromine is not as effective as chlorine. This means that larger quantities are necessary for your swimming pool.

That is why the bromine is often combined with an ozone system or UV light in the pool.

Bromine is also more expensive than chlorine, and its application is more expensive.

But the bromine has one advantage over chlorine: It is not sensitive to UV rays, and therefore no extra stabilizer such as cyanuric acid is necessary.

The bromine also has the advantage that it retains its disinfecting effect even as bound bromine (Bromine that has already reacted with organic substances).

However, this does not mean that no disinfection by-products are created with bromine because bromides and bromoform (bromine-containing THM) are formed when bromine is used.

Nevertheless, the bromine in your pool water can be a useful alternative to chlorine.

It is only important to dose the bromine correctly and test the water regularly.

Bromine is available from pool retailers as slowly dissolving sticks or bromine tablets.

Since the sticks and tablets dissolve slowly, I recommend using a floater when using bromine in the pool.

Tip: You can measure the bromine level in the water using the DPD method. OTO drops also work, but when determining the actual level, the tested level must be multiplied by a factor of 2.25.

For OTO drops: Measured bromine level * 2.25 = actual bromine level.

Biguanide (PHMB) for disinfection in the pool

The PHMB (polymer hexamethylene biguanide) is a chemical molecule suitable for disinfection in your pool.

In the US, it is offered as a biguanide.

It is free of chlorine and highly effective against fungi, germs, and algae, but unfortunately not against sweat or urea.

Therefore, the biguanide is only partially suitable as a disinfectant.

In contrast to chlorine and bromine, there are no unpleasant disinfection by-products such as chloramines or bromides when used.

In addition to the highly effective disinfection, the advantage of the PHMB is that it is mild towards the swimmers and that relatively few quantities are required.

You need 1 liter of the agent for every 10 m³ of water. In a 50 m³ swimming pool, that would be 5 liters.

The biguanide is resistant to UV rays and heat, which means that even a low dosage remains effective in the water for a long time.

In addition, the PHMB only needs to be used in your pool every two weeks, which saves time, effort, and pool costs.

You also don’t have to worry that – as with chlorine – the use will dye your hair green.

However, if misused, the water can become cloudy.

Most PHMB products already contain hydrogen peroxide to kill bacteria and viruses actively.

But if you should use a pure PHMB, then hydrogen peroxide must also be added to your pool.

The use of biguanide is an effective alternative to chlorine and bromine.

However, when using biguanide, you must ensure that the water does not contain chlorine, bromine, or other disinfectants containing silver or copper.

These remedies are incompatible with the biguanide and should never be combined.

This means that when you switch to biguanide, you have to completely change the pool water, scrub the surfaces in your pool and backwash the sand filter.

pH plus and pH minus in the pool

The pH level is one of the most important parameters in water treatment in your pool and expresses the strength of the hydrogen ion concentration in the water.

This means: The pH level shows whether the water in your pool is acidic, neutral, or alkaline.

  • If the pH value is below 7.0, the water is acidic.
  • The water is neutral at a pH of exactly 7.0.
  • A pH level above 7.0 is alkaline (basic).

Ideally, the pH level in your swimming pool is between 7.2 and 7.6 – test strips are sufficient for the measurement.

Water Quality pH Level
Hard pool water > 6,8 – 7,4
Medium-hard pool water 7,2 – 7,8
Soft pool water 7,4 – 8,0
Very soft pool water 7,8 – 8,2

Since rain is always acidic (5.5 – 5.8), the pH level drops during a storm.

If the pH level is below 7.0, metal parts rust, and the joints in the pool are damaged – this is known as corrosive water.

A lower level can be corrected upwards with a pH-Plus granulate.

That’s why a pH+ belongs in every pool chemistry starter set.

The pH level is increased by 0.1 if 100 grams of pH+ granules are used per 10 m³ of pool water. In a 50 m³ swimming pool, that would be around 500 g.

But even if the pH level is too high, problems arise in the pool.

If the pH level is above 7.6, the water in the pool becomes cloudy, and limescale forms.

In addition, the effect of chlorine and bromine decreases.

In this case, use a pH-Minus granulate in your pool.

To lower the pH level in your pool by 0.1, you need 100 grams of pH-Minus granulate per 10 m³ of pool water.

Since the pH level has to be measured almost daily and, if necessary, optimized, it is always worthwhile to have a 5 – 10 kg bucket of pH raiser and pH reducer granules in stock in your pool equipment.

In the worst case, the pool chemistry loses its effect if the pH level is not ideal.

For example, before a pool shock, the pH must first be adjusted so that the chlorine works better. But the pH level also has to be right when using a flocculant in your pool.

The pH level in pool water fluctuates wildly and is influenced by various factors.

To not use too much of the pH plus and pH minus granules, the acid capacity (total alkalinity) must always be measured and corrected to stabilize the pH level.

You will learn more about this topic in the next chapter.

Total alkalinity (acid capacity) in a swimming pool

We talk about acid capacity (acid-binding capacity or acid consumption) in the US, but most products are labeled with the term alkalinity.

The alkalinity (TA) is important for the pH level and expresses the buffer capacity of the pool water.

Therefore, this agent should not be missing in any pool chemistry set.

The total alkalinity should ideally be 80 to 150 ppm in your swimming pool.

For example, depending on the manufacturer, 180 g per 10 m³ of water is required to increase the alkalinity to 10 ppm.

But how exactly does alkalinity affect the pH level in your swimming pool?

It may be that the pH is high, but the pool water is still acidic if the alkalinity is below 80 ppm.

If the pH level fluctuates strongly, you have to test the alkalinity first and, if necessary, correct with the pool chemical I recommend.

Later a pH plus or a pH minus is added to the water to adjust the pH level.

In my blog post, you can read more about the total alkalinity in your pool.

Calcium hardness in the pool

The calcium in the pool water determines how hard or soft the water is.

The calcium level can be relatively high depending on how you fill your pool. For your information, well water has a higher calcium level than tap water.

With a high concentration of calcium, the pool water becomes cloudy.

It also happens that pool walls, ladders, and even the filter sand fog up.

This is prevented by adding calcium hardness to the pool water.

Cloudiness and fogging can occur if the calcium concentration exceeds 600 ppm.

The ideal level for calcium hardness is 200 to 400 ppm. Therefore, 300 ppm is a good average in your swimming pool.

The calcium hardness in your pool is best measured using the photometric and titrimetric methods.

Tip: A high pH level can lead to high calcium hardness. Before optimizing the calcium hardness, the alkalinity and the pH level should first be adjusted.

More pool chemistry that you need

The recommended pool chemistry for disinfecting and optimizing the pH level, alkalinity, and calcium hardness is theoretically sufficient to keep a pool clean.

In practice, however, additional means are required to combat algae, cloudiness, and bad-smelling odors in your swimming pool.

Algaecide against algae growth in your pool

Algae are a well-known problem among pool owners but are usually easy to remove – unless they are black algae.

The algaecide is a chemical agent based on copper sulfate, which can inhibit algae growth in your pool or hot tub.

However, depending on the manufacturer, foam can form in your pool. 

Therefore the non-foaming algaecides are best.

Weekly, one liter per 100 m³ of pool water is sufficient. With a 50 m³ pool, this is 0.5 liters per week.

I recommend always using the algaecide – in addition to the chlorine – in your swimming pool. Otherwise, the water will become cloudy.

In my article, you can read everything from the application to the optimal dosage of the algicide. Simply click on the link.

Flocculant for crystal clear water in swimming pools

The flocculant is a gentle agent that gives your pool water a final touch.

This pool chemical binds the colloidal substances (fine particles) that otherwise cannot be filtered out of the water with the sand filter system.

But the flocculant in swimming pools is also recommended to prevent algae.

The flock pillow is simply placed in the skimmer during use. In the case of a liquid flocculant, 150 to 200 ml/week of flocculant are required per 10 m³ of pool water.

If you want crystal clear pool water, I recommend using a flocculant.

In my blog, you will find helpful instructions on how to use flocculants.

Active oxygen for pool disinfection

The active oxygen is highly effective and gentle pool chemistry. It is suitable as an alternative to chlorine and bromine.

The advantage of using active oxygen is that no chloramines, bromides, or other dangerous disinfection by-products are formed – an application in the paddling pool and whirlpool is ideal.

In addition, there are no bleaching stains, as sometimes happens with chlorine.

For every 10 m³ of pool water, you need 0.5 liters of active oxygen per week.

Unfortunately, active oxygen is quite expensive, and in practice, it is not compatible with chlorine.

That is why I only recommend an application in a whirlpool because the costs are still within reasonable limits.

But of course, that is up to you.

Tip: The active oxygen should always be used in your pool once a week, following the manufacturer’s instructions.

According to chemical experts, overdosing is usually impossible, and a level up to 8 ppm in pool water is considered unproblematic.

Metal remover for the pool

If the pool water is cloudy brown, there is likely a high iron content.

Too much iron and copper in your pool can have various causes.

The water often becomes cloudy, pool stains occur, and rust attacks the expensive pool equipment.

You can easily get rid of this problem with a chemical agent against iron in your pool (Metall-Ex).

You shouldn’t use this type of pool chemistry with a phosphate remover because it will negate the effect.

Usually, chlorine is sufficient for water treatment, but sometimes a metal remover (Metall-Ex) is necessary.

Tip: Under no circumstances use vitamin C against iron in your swimming pool. Vitamin C only has an optical effect and does not remove the iron.

Conclusion: Pool cleaning with chemicals

In the article on pool chemicals for dummies, I showed you all the resources you need for pool maintenance.

The pool chemistry shown is appropriate for the initial filing of your swimming pool and for maintaining the water quality later on.

If you can’t find a pool chemical product in this article, it’s because either it isn’t necessary and would be a waste of money or because it requires a physical process.

One question remains to be clarified: Which of these pool chemicals is the best one?

In practice, chlorine and active oxygen have proven their worth. All other chemicals fail when the water temperature rises above 86 °F.

For me, bromine is not a real alternative to chlorine, as it has a weaker oxidizing power and larger quantities are necessary to keep your pool water stable.

Furthermore, bromine dissolves slowly, and if there are algae in your pool, it still has to be touched up with chlorine.

The resulting by-products such as bromides can only be removed from the pool with a pool shock, and a pool shock contains mainly chlorine or bleach.

When disinfecting your pool, chlorine is the winner and belongs in every pool chemistry set.

But chlorine cannot replace all means of water treatment in swimming pools.

Different pool chemistry is necessary for pH regulation, the optimization of the alkalinity, and the calcium hardness – you can find the products I recommend in the article.

Do you have any further questions about pool chemicals and how to use them?

It’s best to use the search function or contact me at @contactswimfool on Twitter, Facebook, or YouTube.

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Good luck with your pool maintenance, and happy swim!

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Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind swimfool.com, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

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