Pool Chemistry 101

A swimming pool needs a whole lot of attention. With regular cleaning, removal of debris, maintaining the right pH hardness, etc. ensuring that the pool equipment is functioning properly and overall maintenance, it might seem a bit too overwhelming.

Despite all that, owning and maintaining a pool does not have to be intimidating. Let’s dive into the various chemical factors of a swimming pool, the kind of chemicals needed for pool maintenance and the external factors that affect pool chemistry.

pool chemistry

Chemical Factors

For pool water to be safe for swimmers, the water needs to be balanced. This means that the various chemicals that are added to ensure that the pool water is clean and safe should be within their optimal ranges. The following are the various chemical factors of a pool along with their ideal ranges.

pH

‘pH’, which stands for the potential of hydrogen, is a measure that can be associated with an aqueous solution. The pH value of any solution indicates its acidity or basicity.

pH value is measured according to the pH of water, which is neither acidic nor basic, which has a neutral pH value of 7. pH value usually ranges from 0 to 14, with acidic solutions having pH less than 7, while basic solutions have pH greater than 7.

For pool water to be safe for swimming, the pH should be between 7.2 and 7.6, with an ideal value of 7.4. Pool water with lower pH is acidic and can damage the components of the pool as well as cause irritation in the eyes and nose.

Pool water with higher pH can lead to irritation in the skin, cloudiness of the water and could also affect the sanitization property of chlorine.

Alkalinity

The alkalinity of any solution is a measure of the resistance it has towards acidification. For a solution to have a good amount of alkalinity, it should have the right combination of weak acids and their conjugate bases.

This combination of chemicals reacts with other chemicals that get introduced into the water and clean them out to keep the water balanced.

The ideal alkalinity of a pool should be between 80 ppm (parts per million) and 120 ppm. This keeps the pH value of the pool water in check by absorbing the chemicals that might get introduced into the pool from external factors before they affect the pH.

Hardness

The hardness of water is the measure of the amount of lime, or calcium carbonate, present in that water. If the water has a calcium content of less than 100 ppm, it can be categorized as soft water, whereas if it has a calcium content of over 300 ppm, it can be categorized as hard water.

In a pool, the hardness level should be between 200 ppm and 250 ppm. If the water is softer than this range, any external contaminant could introduce calcium into the water that then leeches onto the pool wall and causes corrosion.

If the water is harder than 400 ppm, the calcium carbonate residues can get deposited on the surfaces of the pool and lead to scaling.

Sanitizing Chemicals

To keep the pool water safe for swimming, cleaning out the debris and dirt is necessary, but not enough. Certain criteria need to be maintained to keep pool water safe, which includes regular cleaning, sanitizing and maintenance.

Sanitizing a pool makes the pool water safe for swimming. Sanitizing chemicals do multiple tasks like keeping algae away, killing harmful bacteria and pathogens and maintaining the overall chemical composition in the pool.

Various chemicals can be used to sanitize pool water, some of which are discussed below.

Chlorine

Chlorine is one of the chemicals that can be used to sanitize a pool. Chlorine should be regularly fed into pool water for proper disinfection. It kills a lot of microorganisms that can otherwise cause health issues like athlete’s foot, gastroenteritis and ear infections.

Chlorine levels in a pool need to be tested daily before use as the wrong amount of chlorine can be harmful to your skin and health. The recommended level of chlorine is 3 ppm. Too much chlorine can be harmful to the skin, eyes, hair and lungs.

While referring to pool chlorine, the following terms are often used:

  • Free Chlorine: This is the amount of chlorine that is yet to react with the contaminants. This is an indicator of ‘free’ or ‘unused’ chlorine that is available to act on the microorganisms in the pool.
  • Combined Chlorine: This is the amount of chlorine that has already reacted with the contaminants. It indicates the amount of ‘combined’ or ‘used’ chlorine in the pool.
  • Total Chlorine: This is the sum of the free chlorine and combined chlorine, that indicates the total amount of chlorine in the pool.
  • Stabilized Chlorine: This is the kind of chlorine that does not easily deplete under sunlight. Pool chlorine is available in the stabilized form in pool supply stores but can also be achieved by adding the right amount of stabilizers or cyanuric acid to the pool.
  • Unstabilized Chlorine: This kind of chlorine is not stabilized and thus is prone to depletion due to the UV rays from the sun. If your pool receives a lot of sunlight, the chlorine in your pool water can reduce more easily, resulting in the more frequent addition of chlorine.
  • Chloramine: During the sanitization process, chlorine oxidizes the contaminants, resulting in a chemical called chloramine. Chloramine is the main cause of the pungent smell that is distinctive of an unsanitized pool. To tackle this, chlorine levels should be tested and maintained regularly.
  • Shocking: A shock treatment, or ‘shocking’, is the process of adding an excess of chlorine to pool water such that it sanitizes the pool water more efficiently.

Bromine

Bromine is another chemical that works similarly to chlorine for sanitizing a pool. Compared to chlorine, bromine stays active longer in the pool water. It also has a milder smell and is gentler on the skin and eyes. The recommended level of bromine is 3 to 4 ppm.

Though bromine is more expensive than chlorine, it is ideal to be used as a replacement for chlorine, for those who might have a chlorine allergy. It is also not recommended for use in outdoor pools as it is less effective in the sun.

Biguanide

Biguanide is another sanitizing chemical that can be used in place of chlorine or bromine to kill microorganisms. It is a gentle sanitizer that is often used in dressing wounds and contact lens solutions as it prevents the growth of bacteria effectively.

Biguanide is a lot more stable than chlorine and bromine and is highly effective even under sunlight. When added to a pool, it forms clumps by binding itself with the microparticles and this can be conveniently filtered away.

Biguanide is a lot more expensive than both chlorine and bromine, but it keeps the water softer and has no strong smell.

Ozone

Ozone gas is an oxygen molecule that can be used during filtration of the pool water to kill and/or inactivate viruses, bacteria and parasites living in the water. This acts as a disinfectant that can be easily generated and passed into the pool.

Pool ozone can be generated by a machine known as an ozone generator or ozonator. This can be connected to the circulation and pump system such that it sanitizes the water that gets circulated through the system.

As it works through the circulated water, the actual amount of ozone in the pool water can be extremely low, thus requiring the involvement of other sanitizing chemicals.

Other Chemicals

Apart from these sanitizers, some other chemicals help to maintain the chemistry of a pool. These too act as sanitizers, but for more specific purposes such as removing microscopic particles, metal particles and algae. Certain chemicals, mentioned below, help to prevent the depletion of chlorine in harsh sunlight.

Clarifier

Pool water can get contaminated by a lot of minute particles that might be too small to sink to the bottom of the pool or get filtered during circulation. These can include organic matter, bacteria and other microorganisms.

By adding a clarifier to the pool water, these particles get attracted to the clarifier particles and the clump together, making them visible and easier to remove.

After adding a clarifier, it can take several days to efficiently remove all such particles. The clumps float on the surface of the pool water and can be skimmed easily.

Flocculant

When most pool sanitizers fail, flocculant can come to your rescue. Flocculant, also known as pool flocc, is a chemical that efficiently eradicates unnecessary particles from the pool by clumping them together, making it easier to filter them out.

When flocculant is added to pool water, it almost immediately attracts such particles and creates larger clumps that are heavy enough to sink to the bottom of the pool. These can then be easily removed using a pool vacuum.

A flocculant is recommended when you want to clean up your pool within a few hours.

Cyanuric Acid/Stabilizer

Stabilizers protect the chlorine in pool water such that it does not get depleted due to the sun’s ultraviolet (UV) rays. Depletion of chlorine makes the pool water unsafe to use as the water does not get sanitized easily.

Indoor pools do not need stabilizers as they are not exposed to sunlight. For outdoor pools that receive a lot of sunlight, the stabilizer level should be 60 to 80 ppm.

Cyanuric acid is the most commonly used stabilizer. It shields free chlorine easily and effectively, but too much of it can bind with the chlorine, thus reducing the effectiveness of chlorine in the pool.

Metal Sequestrant

Too many metal sediments in pool water can significantly affect the health of swimmers. Metal in pool water usually gets introduced from the source water itself and is difficult to filter out. It is also quite difficult to detect metal in pool water as it only becomes apparent much later, after causing stains on pool surfaces and equipment.

If you have too many metal contaminants in your source water, it is advisable to add a metal sequestrant. Metal sequestrant particles are invisible and do not affect the composition of the water directly.

However, they bind with any metal particles in the water, preventing the metal from depositing on the pool’s surface.

Metal sequestrant particles eventually break down, thus reducing their effectiveness. So it is advisable to add metal sequestrants to your pool weekly or monthly, based on the amount of metal in your source water, and make this a part of the pool maintenance routine.

Algaecide

Algae is a living water plant that can create a slimy green layer on your pool water. This can also clog your pipes and filters, leading to poor water circulation. Algae thrive in warm water and make sanitization very difficult.

They multiply very fast and can even cover your entire pool if not treated in time. This is why algae in a swimming pool need to be eradicated at the first sight.

Algaecides, as the name suggests, are chemical compounds that can kill algae. They also prevent the algae from further multiplying by disrupting the cell division.

Though algaecides should not be used regularly, they should be used at the start of the season and at other times only when necessary.

Muriatic Acid

pH value greater than 7.6 makes the pool water too alkaline and can make the water cloudy and unhealthy. This makes the chlorine less effective and can also increase the rate of scaling.

Muriatic acid is a diluted form of hydrochloric acid that is commonly used to remove salt deposits or stains. It helps to maintain the pH levels in your pool by reducing the basicity. It should be diluted in the ratio of 1:10 acid to water as it can be too acidic to be added directly.

Muriatic acid is a harsh acid that should be handled with care. Before using muriatic acid, wear proper protective gear to cover the skin and eyes and exposure to this acid can cause severe burns.

What Affects the Chemical Balance of Pool Water

Several factors affect pool chemistry, which is why pool water needs to be tested often and maintained at the prescribed levels. Maintaining pool chemistry is essential to keep the pool safe to use. Here are the several factors that affect pool chemistry.

Body and Hair Products

Most of the contaminants in pool water can come from the products on our bodies. Sunscreen, shampoo, soap, lotion, perfume, etc. are all chemical compounds that can react with pool water and contaminate it.

This is why it is advised to take a shower before getting into a pool to reduce the chance of introducing these contaminants to the pool.

Pets

Experts believe that a single dog can have the same effect on pool water as almost three human beings! Dogs shed a lot of hair in general, and this gets accelerated in a pool.

Loose hair can block internal plumbing and affect the filtration process in the pool. Also, their coat could carry a lot of parasites, dirt and mud that get loosened in the water and mix with the water as they swim around.

Dogs also have relatively sharp nails that could tear any plastic or vinyl lining in a pool and also damage other pool equipment.

To reduce these effects, trim your dog’s nails regularly and brush their coat and rinse their body with water before letting them in the pool.

Contaminated Source Water

If your pool water tends to get imbalanced too often, the culprit could be the source water. Source water could contain a lot of metal, minerals as well as organic matter that can instantly contaminate your pool. This is why it is necessary to install a filter at the source to reduce such contaminants.

Despite filtration, source water could still carry these contaminants, which is why regular testing is necessary. Pool water should also be tested every time it is refilled as the chemical balance can get disrupted.

Rain

Rainwater is slightly acidic and can easily affect the pH of the pool. The pH of rainwater is lower than 7.0, so if there is heavy rainfall, the pH of your pool could reduce drastically.

As mentioned earlier, acidic pH can be quite harmful to swimmers as well as the various surfaces of the pool.

A good way to reduce contamination due to rain is to keep your pool covered when not in use. Also, test your pool water after a rainfall and maintain the pH level if needed.

UV Light from the Sun

Sunlight consists of light at various ranges, including UV light. UV light affects the chlorine consumption in the pool water. During the hot summer months, the amount of UV rays in the sunlight is high and the chlorine level can drop quickly, making the water unsafe to swim in.

Stabilizers or cyanuric acid can be used to shield the pool from harmful UV rays. These act as a sunscreen to the chlorine present in the water, thus protecting the chlorine from depletion.

Organic Matter and Debris

Organic matter such as leaves, hair, sweat, dead skin, etc. also harms the pool water. These can introduce phosphates into the water which directly affects pool chemistry.

Phosphates can also come into your pool water from any organic matter in the pool’s vicinity. If there are any algae in your pool, phosphates act as their food and thus, promote their growth. This, in turn, reduces the chlorine in the pool water as the chlorine gets consumed to clear the algae.

To avoid this situation, keep the surroundings of your pool clean. Skim the water regularly and remove organic matter in and around the pool as soon as you spot them.

Also, as tempting as it might be to have a pool snack, avoid food and beverages in the pool.

Wind

A lot of organic matter, algae and other unwanted items can get into your pool on windy days. For an uncovered pool, a lot of dirt and debris get carried in by the wind and get deposited on the pool’s surface.

This then affects the chemistry of the pool water, by introducing phosphates into the pool, as mentioned earlier in this article.

Heat

If you have a heated pool, it can quickly turn into a breeding ground for bacteria. At water temperatures higher than 90°F (32°C), bacteria growth increases, leading to unsanitary conditions.

This can also lead to scaling on the pool surfaces and equipment, affecting the longevity of your pool.

To avoid such conditions, always monitor a heated pool and test and adjust the water composition frequently.

Balancing Your Pool Water

With all of this information in hand, the question arises as to how do you achieve balanced pool water? To achieve the right balance in your pool water, here is the correct order of tackling the composition:

  • First, measure the alkalinity and adjust it to lie between 80 to 120 ppm.
  • Next, ensure that the pH of the pool water is between 7.2 to 7.6.
  • After achieving the right pH, check the hardness of the water and bring it to 200 to 400 ppm.
  • Once the pool water is at the right hardness, adjust the chlorine level to 3 ppm.
  • Finally, ensure that the total dissolved solids are not more than 2,000 ppm.
  • Turn the pump on and let this water circulate. After an hour, test the water again and make further adjustments if necessary.

Summary

A lot of effort and money goes into owning a pool, but without proper maintenance, you could end up spending a lot more to keep the pool running. With the proper knowledge of pool chemistry, owning and maintaining your pool should be a breeze.

Take the right measures and precautions upfront and you will be able to avoid a lot of complications. Have a safe swim!

michael keenan author

Author - Michael Keenan

I'm Michael Keenan the owner and creator of the Outdoor Care Guide. I'm a trained horticulturist with over 30 years experience in pool care, plant care and landscape care! Seemed like a good idea to share - I think I can make your life easier and save you some time and money!