Beginner’s Guide to Pool Water Chemistry 

Most people believe owning a pool is a ton of work. However, owning a pool doesn’t need to be a second job. Yes, maintaining a clean pool requires some work. However, if you understand your pool’s water chemistry, your life will be much easier, and you don’t need a degree in pool water chemistry to do it.

Four main components go into a pool’s water chemistry. Chlorine, pH, alkalinity, and calcium hardness levels all factor into your pool’s water chemistry. Having good water chemistry is what makes a pool clean and safe for people and animals of all ages to enjoy.

If you’re looking for a complete beginner’s guide to pool water chemistry, you’ve come to the right place. In this article, we’ll go over proper levels for chlorine, pH, alkalinity, and calcium hardness, as well as what happens when these levels are too low or too high. We will also discuss how to even out these levels when needed.

You don't need to be a professional chemist to balance your pool's water chemistry

Chlorine in Pool Water

Chlorine is added to pools to kill germs. When chlorine is added to a swimming pool, it forms a weak acid called hypochlorous acid. Hypochlorous acid kills bacteria such as salmonella and E. coli, as well as viruses that may cause swimmer’s ear and diarrhea.

What should pool chlorine levels be? 

Pool chlorine levels should remain between one part per million and three parts per million of free chlorine. Free chlorine is the amount of chlorine that is not bound to microbes and chemicals in the water. Therefore, free chlorine remains available to eliminate microbes and neutralize contaminants.

If you want to test your pool’s free chlorine levels, I recommend the Taylor K2005 Swimming Pool Test Kit. The kit includes everything you need to test the chlorine levels in your swimming pool. This is an easy way to keep an eye on your pool’s water chemistry in just a few minutes.

What happens if chlorine is too low?

When chlorine levels in a pool are too low, it becomes too diluted to do its job. As discussed above, chlorine is responsible for eliminating algae, bacteria, viruses, and other harmful organisms from your pool. When the chlorine in your pool is not doing its job, swimmers are at risk for illnesses and infections caused by these harmful organisms.

What causes low chlorine?

If you consistently see low chlorine levels in your pool, you may have an infestation. Algae, fungus, or bacteria infestations can eat up the free chlorine in your pool. Check your pool for visible signs of algae growth. You may still have microscopic organisms eating your free chlorine if you don’t see any. Try The Original Watersafe Rapid Bacteria 10 Test Kit to test for coliform and non-coliform, E.coli, salmonella, pseudomonas, shigella, and other forms of bacteria.

Another cause of low chlorine levels in a pool is the UV rays produced by the sun. When chlorine is exposed to UV rays, the ions in the chlorine begin to separate, which causes them to deteriorate. While this may sound like a lot more chemistry than you signed up for, it means that exposure to sunlight causes chlorine levels to decrease. 

How to raise pool chlorine 

To raise the chlorine level in your pool, you need to add more chlorine. I recommend the In The Swim Chlorine Tablets to boost chlorine concentration in your pool. However, if you don’t know why your pool is eating your chlorine, you will throw money away by buying more chlorine. So, the first thing you need to do is figure out why your chlorine is disappearing. Once you have figured out the cause of your lowered chlorine levels, there are a few things you can do. 

If you’ve realized the lowered chlorine levels are due to UV exposure, you should try limiting the amount of sun your pool is getting. This may seem impossible because you can’t move the location of your pool into the shade. However, you can move the shade to your pool. If you can, installing a Shade Sail over your pool will block harmful UV rays from your pool and keep the temperature down. Another option to try and reduce your chlorine loss is to use Cyanuric acid. This acid acts as a sunscreen for pool water and chlorine. When this runs low, the chlorine will burn much faster. You can test for this acid in the Taylor pool test kit recommended above.

If you’ve realized algae or other organisms are eating your chlorine, you need to get rid of the organisms. First, according to Lowes’ pool tips, you should clean the pool and the pool filter, then shock the pool. Once you have done this, you can test the water again, add algaecide, then brush and vacuum the pool again. 

If you own a saltwater pool, you should be able to simply increase your chlorinator output or put it on a 24-hour boost mode to raise chlorine levels. In addition, in saltwater pools, low salinity can be what causes low chlorine levels. If there are not enough salt molecules parts per million for the chlorinator to turn into chlorine, which leads to low chlorine levels.

What happens if chlorine is too high? 

Excessive amounts of chlorine in a swimming pool can also have negative effects. One of the most adverse effects of increased chlorine levels is that they can alter the pH level of the water, making the pool more acidic. 

When the chlorine level is too high, swimmers may experience a red, itchy rash with bumps, eye irritation, and overly dilated blood vessels in their eyes. In addition, continuous exposure to high chlorine levels can cause sickness and injuries such as coughing, nose or throat pain, extreme eye irritation, and cloudy or foggy vision.

What causes high chlorine?

High chlorine levels can be mainly attributed to human error. If you add too many chlorine tablets than necessary during cleaning or shocking, your chlorine levels will directly reflect that. Your levels should even out after about 24 hours, depending on how much extra chlorine was added.

How to lower pool chlorine 

As stated above, chlorine levels should even out in about 24 hours. However, if you want to aid the process, there are some things you can try. Adding fresh water to your pool will dilute the concentration of chlorine. If your pool is full, drain some water to create more room. 

You can also add some chemicals to neutralize the chlorine, such as sodium thiosulfate and pool-grade hydrogen peroxide. If you decide to add these chemicals, follow instructions; if you misuse them, you may make your pool worse than it was, to begin with. 

pH in Pool Water

The pH of a pool is the measure of its acidity. Measuring pH is done on a scale of 0 to 14. A pH below 7.0 indicates an acidic pH, and a reading above 7.0 indicates a basic pH. There are many factors that affect the pH of your pool, but it is incredibly important to keep your pool water at a safe pH level.

What Should Pool pH Be? 

Your swimming pool’s pH should maintain a level between 7.3 and 7.6. Keeping your pool within a pH range of 7.3 and 7.6 will maintain a pool that is clean and safe water. If your pH drops below 7.0, it is too acidic. If your pH rises above 7.8, the water is too alkaline.

What Happens if Pool pH is too Low? 

Low pool pH means that your pool is too acidic. Exposure to acidic pool water can cause plaster, grout, stone, concrete, and tiling to break down. Vinyl surfaces can also wear down and become brittle, which puts your pool at risk for cracks and tears. Breakdown of these materials will lead to cloudy pool water.

What Causes Low pH?

Low or acidic pH in pool water is mainly caused by excess chlorine along with environmental factors. Environmental factors include acid rainfall, leaf or tree debris, and dirt or grass that make the pool water more acidic. These all have a pH level of about 3, which lowers the average pH of your pool water. 

How to Raise pool pH

Luckily there is a fairly simple way to raise the pH of your pool water. Using baking soda is a great way to raise your pool’s pH! Using 1.5 lbs of baking soda per 10,000 gallons of pool water will increase pH by ten parts per million. If your pool’s pH tested below 7.2, add 3-4 pounds of baking soda.

What Happens if Pool pH is too High? 

A pool with a too high or too alkaline pH has a measurement of above 7.8. This can have adverse effects on swimmers and the pool itself. For example, swimming in an overly alkaline pool may cause skin rashes. In addition, pool water may appear cloudy and dry with a scaly appearance on pool equipment.

How to Lower Pool pH 

You can lower the pH of pool water with chemicals or naturally. For example, adding chlorine tablets to your pool will raise the pH. If you don’t want to add a bunch of chemicals to your pool, you can do it naturally by draining some water out of the pool, and refilling it with water of a lower pH will have the same effect.

What Causes High pH? 

Many things can cause high pH. Algae is a big thing to look for if your pool water is having consistently bad readings. (To get rid of algae, follow the same steps listed in the chlorine section.) If you have recently added cleaning chemicals to your pool, that might be the reason for the high readings. A sudden increase in pool water temperature is another thing that may cause a higher pH. This temperature increase could be because of a water heater or even a week of hot, sunny days.

In saltwater pools, chlorination is constantly taking place. This makes it very easy to maintain proper chlorine levels. However, this causes pH to constantly rise. To mitigate this, you should add a cup of sulfuric acid to your pool every few days.

pH imbalance can cause filters to clog up

Alkalinity in Pool Water

Alkalinity is a way to measure how well a pool is performing in neutralizing acids and bases. While this sounds complicated, it just means that your pool is maintaining a stable, safe pH level. That said, alkalinity is very important in maintaining a clean and safe pool.

What are proper alkalinity levels?

The alkalinity levels in your pool water should stay in a range between 80 and 120 parts per million. Setting and keeping the alkalinity of your pool within 80 to 120 parts per million will give your pool the ability to resist a change in pH and keep it at the proper baseline.

What happens if alkalinity is too low?

Low alkalinity in pool water can have detrimental effects on a swimming pool. Exposure to low alkalinity pool water may cause the walls of your pool to delaminate, crack, or become etched. Metal surfaces exposed to water with low alkalinity may melt due to the corrosive properties of the water, which can cause stains on the pool walls around the fixtures.

In addition to the risk of pool damage, swimming in water with low alkalinity is dangerous to people and dogs. Swimming in acidic water may cause irritation to the skin, eyes, nose, and throat.

How to raise alkalinity 

There are two main ways to raise the alkalinity of your pool water, but they are pretty much the same thing. Most pool stores carry alkalinity increaser products that are way overpriced because they are marketed for pools. All of these alkalinity increasers have one main ingredient: sodium bicarbonate a.k.a. BAKING SODA! If you buy sodium bicarbonate in bulk, you will save yourself a few bucks.

What causes low alkalinity?

Pool water with low alkalinity can be due to a variety of causes. If you’ve had a bunch of rainwater running off into the pool can dilute the water, which drives down alkalinity levels. If you haven’t had much rain and your alkalinity is still lowered, it may be due to the bodily fluids of swimmers, such as sweat and urine. 

What happens if alkalinity is too high?

High alkalinity levels can cause problems for your pool and its patrons. High alkalinity means an unstable pH level. This can cause high calcium levels. Raised calcium levels can lead to clogged filters, scaling, and cloudy water. It can also cause itchy skin and eyes for swimmers.

How to lower the alkalinity 

To fix the high alkalinity in your pool water, you are going to have to add acid to your pool. Muriatic acid, or hydrochloric acid, is the best way to lower a pool’s overall alkalinity level. Hydrochloric acid has a pH level between 1 and 2, so it is a great way to raise your alkalinity as well as kill mold and remove rust and calcium deposits. 

What causes high alkalinity?

Unfortunately, sometimes when you try to fix one thing in your pool, something else is affected by it. One of the most common causes of high alkalinity is because you tried to use sodium bicarbonate or baking soda to raise your pool’s alkalinity. Another cause of high alkalinity is it can come straight from the source. If you’re using fill water with high alkalinity, you will have similar levels in your pool water.

Calcium Hardness in Pool Water

Calcium hardness is a way to measure the number of calcium ions in your pool water. When you hear people talk about hard water, they are referring to water with high mineral content. The term calcium harness refers to minerals in the water, including calcium, magnesium carbonates, bicarbonates, chlorides, and sulfates. 

What are proper calcium levels?

The calcium hardness levels in pool water should stay within a range of 200 to 400 parts per million. These levels need to be monitored closely and actively managed to maintain a clean and safe swimming pool. If your pool is out of the safe range, you will notice cloudy water.

What happens if calcium hardness is too low?

If your pool water’s calcium hardness levels are under 200 parts per million, it can ruin your pool’s alkalinity. This has the ability to corrode metal fixtures and clog mechanical parts in your pool. Soft water will also cause long-term damage to plaster, vinyl liners, and grout. 

How to raise calcium hardness

Luckily, raising calcium levels is fairly simple. Calcium increasers that contain calcium chloride are the best option to raise your calcium hardness. You can order a calcium increaser online or at a local pool supply store.

What happens if calcium hardness is too high?

Pools with high calcium hardness commonly appear cloudy or murky. Hard water appears murky due to the excess minerals floating around. These minerals can cause the water to scale in and around your pool and your equipment. This can clog your filters and block the flow of water to and from your pool.

How to lower calcium hardness

Unfortunately, lowering the calcium hardness of your pool water is not nearly as easy as raising it. The process of softening water is done using ion exchange resins to remove calcium, magnesium, and other minerals from the water. This process is typically done with a water softening filter.

If your pool is not clear you may have calcium buildup

Quick Reference to Pool Water Chemistry

We’ve talked a lot about the different factors that make up the chemistry of pool water. Check out this quick reference guide to the basics of pool water chemistry.

NameProper levelsWhat happens when too lowWhat happens when too highHow to increase
Chlorine1 – 3 parts per millionBacteria, algae, and other harmful organisms in your pool are not killedpH can become more acidic, causing irritation to swimmersAdd chlorine tablets
pH7.3 – 7.6Breakdown of pool fixtures may cause breaking in vinyl surfacesBuildup on pool equipment and irritation to swimmersAdd 1.5 lbs of baking soda per 10,000 gallons of pool water
Alkalinity80 – 120 parts per millionBreakdown of pool fixtures and surfacesCan cause calcium buildup and cloudy waterAdd sodium bicarbonate
Calcium Hardness200 – 400 parts per millionDamages plaster, vinyl liners, and groutMurky pool water. Can clog filtersAdd calcium chloride

When dealing with pool chemicals, there are some that can be very dangerous when stored together. Check out our list of pool chemicals that should never be stored together to keep you and your family safe.

Final Thoughts

Owning a pool is a big commitment, but it doesn’t need to be a full-time job. Doing a little bit of work a few times a week and monitoring your pool levels will save you a lot of time and money. If your water chemistry gets out of control, you will have damage to your pool and your pool equipment, and your swimmers will have irritations too.


Chicago Tribune: Yes, you can put too much chlorine in a pool

CDC: Healthy Swimming

New York State: The Facts About Chlorine

Lowes: How to get rid of pool algae

Arm and Hammer: DIY Pool Maintenance Tips