Swimming Pool Chemistry Guide

Swimming Pool Chemistry Guide

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How important is chemical balancing in pools and spas? As a swimming pool and hot tub expert I can not stress to you how important understanding and maintaining your pool and spa chemical treatments is to both the health and well being of the bathers and also the longevity of your pool equipment. To highlight the extreme end of the spectrum poorly treated water can actually kill you and chemical balance can ruin expensive items like a new pool heater in as little as a few weeks - and the manufacturer will not give you a warranty replacement as they will be able to see the chemical damage which is not covered under any manufacturer warranty.


You can learn most of what you need to know about balancing your water in 10 minutes right here on this page so there is no excuse to not understand how it all works. Admittedly the rabbit hole goes pretty deep when you really start to analyze what is happening in the water and what different situations can happen. For the most part, pool and hot tub owners will only need to know some basic core information about water balancing and this will cover over 95% of the real life situations you will actually encounter caring for your pool or spa. Learning just a little about the order of chemical corrections as well as which levels you need to watch the closest will go a long way towards helping you with the initial learning curve for water chemistry and balancing.


Note* I have added a series of videos to this page to help you learn these concepts. If you watch the videos it will now take you longer than 10 minutes to get through this information on pool and spa water chemistry and balancing.

Easiest Way To Learn Pool Water Chemistry

This video is a stand-alone lesson on pool water chemistry that takes an unconventional approach to teaching conventional technical process. In short, you can learn how to manage most of your water chemistry from this one video that explains concepts behind water chemistry and not just the numbers. If you have been having trouble learning about pool water chemistry then definitely give this video a chance and you might find you understand a lot more after watching this.

If you only watch one video about water chemistry from this page then make it this one!

What Is The Point Of Balancing Pool & Spa Water?

There are many people who claim to never balance their pool water. They say that they add chlorine once a week and that is it - this is something that you hear all the time working in the pool and spa industry. They also say they can tell if the water is balanced just by looking at it (scientifically, fundamentally not true).

Taking this approach to water balancing is the equivalent of saying putting gas in a car once per week is all you need to do, and you can tell if a car is broken by looking at it. Being ignorant of the importance of chemical water balancing in swimming pool and spa water will not help you to get over a bout of legionnaires disease, to say the least. It is also important to note that having poorly balanced water can also expose you to risk for long term health problems. Chlorine in particular is something that you can be exposed to 10x to 20x more of in a poorly maintained pool than a well balanced pool. Multiply that exposure over the lifetime of a pool owner to begin to see how balancing your water is a trouble worth taking. Don't make the mistake of thinking that a chlorine free pool is a healthier option. The healthiest option, easily, is learning to use traditional methods of sanitizing and balancing and to learn them properly. If you want to learn more about this you can read this article that looks at the secrets to the best pool water.

How To Take Care Of Your Pool & The Order To Do It In

A big part of the problem as a new swimming pool owner, or someone new to caring for and maintaining a pool, is simply knowing the priorities and the order of operations that you should use when approaching the maintenance schedule. This video goes a long way to help you learn quickly about where the maintenance priorities are for pools and what tasks you should be completing (such as vacuuming, water testing, filter cleaning).

The actual time needed to take care of a swimming pool is not very much. Measured as perhaps a half hour or an hour total every week. Of course there is a learning curve to maintaining pools, understanding water chemistry and how all of these things work together. With some practice and the help of these videos soon you should have very little trouble keeping your pool clean and clear at all times.

Basic Water Chemistry Values

The values shown here are the minimum that you need to memorize. While these represent just the tip of the iceberg in terms of pool and spa water chemistry, keeping these values within the tolerable range shown here will resolve over 90% of all water balancing problems that you will likely encounter.

Additional Water Chemistry Values

These secondary values are water chemistry variables that you do not deal with as often however they are also very important to maintaining your pool and spa water properly. Iron in pool water can cause brown staining and brown pool water and copper can cause emerald green pool water (or green hair in swimmers). Metals can be from source water or from chemicals like algicides or copper and silver ionizer systems and are responsible for the majority of stains in your pool. Phosphates are a food for algae and promote voracious algae and plant matter growth in your water. Above 500 ppb you will notice chlorine being depleted more readily. Above 1000 to 2000 parts per billion you will struggle to hold a chlorine residual.

Chlorine In Swimming Pools

Chemical sanitizers like chlorine and bromine are the primary line of defense against harmful pathogens that can grow in pool and spa water. We could use chemicals other than chlorine (bromine) in pool water but they all lack one or more critical component that we need a chemical sanitizer to have. It is not enough to just help keep the water clean...it is important how it keeps the water clean, and also how long it takes to work. There are many chemicals that can partially keep pool water safe. Chlorine is rare as it achieves all four of these important points:

1) Be a sanitizer
2) Be an oxidizer
3) Be an algaecide
4) Build a residual in the water

The only chemical sanitizers that meet all four of these requirements are bromine and chlorine. There are a host of other chemicals and alternative products that can provide some of these properties however they all are missing at least one. For this reason chlorine and bromine are used despite them being potentially harmful themselves. In moderated doses these sanitizers are the lesser of two evils when compared to dangerous bacteria and viruses that grow in unsanitized water.


There are a host of "alternatives to chlorine" in that there are options that do some of the things that chlorine can do to protect your water. It is important to understand that even new technology systems like hydroxyl radical based AOP systems or reliable older technology like germicidal UV lights still lack the ability to do everything that chlorine can do. The same can be said for every other system on the market that does not use chemicals sanitizers like chlorine in that they probably work to help the water, but not as effectively as chlorine and the four layers of protection it provides.

Saturation Index Balancing Pool Water

In this video I start with talking about calcium hardness, which is important as this is one of the fundamental chemicals we monitor in pool water, but quickly I move on to saturation index. LSI refers to Langelier Saturation Index which is a measurement of water condition based on a scale of acidic (corrosive) state, neutral state, or scaling state. Calcium hardness is just one of a handful of chemical parameters used to calculate the saturation index. The reason that this needs to be balanced in pool and spa water is to improve water quality and to prevent potential damage to the pool and pool equipment.

Calcium hardness in pools - As you are probably familiar there is a difference between hard and soft water like you see with city water supplies vs. country well water supplies. One of the most defining differences is how easily bubbles form in soft water. "Soft water" has a low calcium hardness level, often 0ppm and this would cause a huge amount of bubbles in swimming pools and especially hot tubs even from the smallest amount of impurities or detergent in the water. This is obviously something that you do not want in your pool or spa.

Even more importantly however is the fact that if you do not maintain the correct amount of calcium in your water then the water will seek to balance itself by leeching minerals from concrete, stone and metal components in your swimming pool. While outside of the scope of this basic water balancing crash course if you would like to know more about why calcium levels can damage your pool you can research "saturation index" which is a complex calculation to help determine if water is in a neutral state, scaling state or acidic state. This calculation factors in water temperature, calcium levels and pH levels and the primary variables that effect the state of the water.

Balancing pH and Total Alkalinity

This is where the wheels come off. The relationship between pH and total alkalinity in pool and spa water is where over 90% of water problems begin and end. If you are going to struggle with any concept of chemical balancing this is where you will have a problem - but it does not need to be this way. When explained in a way that makes sense it is easy to see how these two values work together and the importance of each.

What is pH?
pH is the scale that represents the relationship between acids and bases in your pool. The scale runs from 0 (extremely acidic) to 14 (extremely basic, or alkaline) with the range of 7 being "neutral". What defines "neutral acidity" is actually us. People. We are attempting to match the pH of the water to the pH of the human eye (7.5) as this produces the most comfortable bather experience. Super simple.

What is total alkalinity?
Total alkalinity is the measurement of how much alkaline material (basic material, opposite of acidic) is in the water. The technical description is that alkalinity is the buffer for the pH levels. Without the alkalinity in the correct range you will not be able to control the pH of the water.

What is the relationship between pH and total alkalinity?
If you had a body of water with a pH of 7.4 and an alkalinity of 0 the problem is that adding any material with a pH OTHER than 7.4 will drastically change the pH value. There is no buffer. While you are able to "balance" your pH level the introduction of lower or higher pH materials to the water will have a very large impact on the overall pH level.

Now consider that you have a pH of 7.4 and a total alkalinity level of 100ppm. What this means is that there is 100 parts per million of alkaline material in the water already "balanced" against 100ppm of acidic material already in the water. The addition of higher or lower pH materials into the water will have less of a total effect on the pH.

The part where is starts to make sense: Without an established level of alkalinity in the water the introduction of any new alkaline or acidic materials will change the pH drastically. At 100ppm total alkalinity there is already so much alkaline AND acidic material in the water the addition of more represents only a small percentage of the total amount already in the water - resulting in little or no change to the actual pH levels. Total alkalinity is the buffer for pH in pool and spa water. See that wasn't so hard, was it? This now leads us to a very important aspect of pool and spa balancing which is the order that you correct your chemicals in. This is a subject that even many pool professionals do not seem to understand fully.

What Order Should I Correct My Pool Chemicals In?

The order of chemical correction when balancing water is one of the most important parts of the process. You could do everything else correctly but adjust your chemicals in the wrong order and you will always have trouble maintaining your water balance. Many swimming pool "professionals" and long term pool owners do not follow this important rule and so you may find other people giving contrary advice about this subject.


1) Alkalinity

2) pH

3) Calcium hardness

4) Chlorine (or bromine)


If you understood the explanation of how pH and alkalinity work together it should be clear why the alkalinity needs to be brought into range first before pH. If you adjust the pH to be correct first, the pH will change when you adjust the alkalinity. When making alkalinity and pH corrections it is important to understand that adjustment to either level will affect both the pH and alkalinity levels in almost every case. There are very few ways in which you can affect or change one number without the other also changing.


Alkalinity and pH example - If you had a high pH and low alkalinity levels (like commonly encountered with salt water systems) you would need to correct the alkalinity to the high end of the ideal range, 125ppm before correcting the pH. This will allow you to then make a pH correction to lower the pH, which will also lower the alkalinity levels. When you are finished the alkalinity level should be somewhere in the middle to high end of the ideal range. Conversely if you only brought the alkalinity level up to the minimum, 75ppm, when you correct the pH down into range next the alkalinity will drop and now be outside of ideal levels. You need to understand that when you adjust the pH second, whatever direction you move the pH you will also see the alkalinity move in that direction. For this reason you slightly overcorrect the alkalinity in the opposite direction of the direction you are going to adjust the pH next. Once you get your head around how to adjust your pH and total alkalinity levels everything else is easy by comparison.

What Is The Importance Of Cyanuric Acid & Pool Stabilizer

30-50ppm ideal - CYA, cyanuric acid, water conditioner and stabilizer are all ways of saying the same thing. This is the protection that is needed to prevent your sanitizer from being broken down by UV light. Since chlorine is expensive and very important in the water using stabilizer is required to make sure that you are able to maintain chlorine levels.

If the cyanuric acid level gets too high, over 80-100ppm, you can experience a reduced effectiveness of your sanitizer despite having measurable chlorine levels in the correct range. This is how bacteria and algae can grow in a swimming pool with acceptable chlorine levels. If you have a problem with green water despite having good sanitizer levels then you should double check that you do not have too much stabilizer. Since stabilized chlorine have cyanuric acid added to them, such as chlorine pucks or granular chlorine, continued use of these products will raise cyanuric levels slowly over time. When the CYA levels get too high dilution with fresh water is the only method to reduce the stabilizer levels back into ideal range.

How Do You Add Chemicals To a Pool?

A very common question from new pool owners is in regards to actually adding the chemicals to the pool. Is there is a process or specific way that you are supposed to do this? In short, yes. Firstly, pool chemicals can be dangerous if they interact directly so you should never add more than one chemical to a pool at a time. Leave many hours in between chemical corrections ideally, but a minimum of one hour between differing chemicals would be a good idea.


The correct way to add a chemical will depend on which chemical exactly you are working with. Fortunately all pool chemicals must be sold with dosing instructions and handling instructions so you can always (should always) defer to the instructions from the manufacturer. In general, some products are less concerning to handle and add to the pool. For liquid products like liquid chlorine I prefer to pour slowly in front of a strong flowing pool return. For granular products like cal-hypo chlorine I dissolve in a dedicated bucket so that you can ensure the granules of chlorine do not sink to the bottom and stain or damage your pool surface. Essentially, do not mix chemicals or harm yourself accidentally handling them, and do not allow any chemicals to just sink and sit on the pool floor. Use a brush on your pool pole and brush any chemicals which fail to dissolve when you add them to the pool.

What Are Phosphates In Pool & Spa Water?

Phosphates are a complex problem that can be summarized by saying that phosphates act as a food supply for algae allowing advanced growth of algae in the water. This would make it difficult, and sometimes impossible, to maintain water clarity regardless of other chemical levels. Phosphates can also cause algae growth even when there is free chlorine available in the water to prevent this from happening.

At 200 to 500ppb, parts per billion, phosphates begin to have a noticeable impact on water quality. At 1000ppb or more the ability to control algae in the water is almost gone completely and corrective action must be taken to control the phosphate levels in the water. While it may not be possible to prevent phosphates from getting into your pool water it may be a good idea to try to locate the cause of your increased phosphate levels. Using phosphate removal chemicals are the only other option and as one of the most expensive individual chemicals you want to limit how often you need them. Even if you do not think you have a problem with phosphates you should have your water tested for this at least every spring.

How Often Should I Test My Pool & Spa Water?

Until you have gained some experience with maintaining a chemical balance in a pool or hot tub you should plan on testing the water often. Constant testing will help you to learn more about the nature of interaction between your chemicals and fast track you to easy water care. When just learning how to balance your pool or spa you should test the water every day, sometimes even twice per day, just to help see the process that happens when you make a chemical correction.

Since most chemicals that you add take effect in the water slowly over time you need to allow time in between corrections. A minimum of 12 hours, and ideally 24 hours, should be left in between chemical adjustments. This will help you to avoid over correcting your chemicals which will cost you time, money and frustration. While test strips are quick and easy and good to have on hand for quick reference it is a good idea to invest in a DPD test kit for more accurate water testing at home. Additionally you should locate a water lab to have them double check what your readings are showing however a word of caution is that not all water labs are created equal and many have a reputation for having you buy and use countless products that you do not actually need.





Taylor K2005 Water Test Kit


I use pool test strips too sometimes especially for a fast check of chlorine levels. Be aware that test strips are not suitable as a stand alone pool water chemistry testing system. You will need to have more accurate water testing done at a local water lab - but if you prefer at home testing then the gold standard, by far, are Taylor Technologies water test kits like the K2005 kit pictured above. There are a few different water test kits from Taylor Technologies but an abbreviated buyer's guide is the 1000 series test kits are very small and limited. I endorse the K2005 test kit for pool owners and the K2006 test kit for pool technicians. Purchase K2005c or K2006c for larger reagent bottles if you do a lot of water testing.


Well...that's it! This page represents the bare minimum that you need to understand about pool and spa water chemistry in order to safely balance your water. There are many situations that fall outside of this basic information however this is intended to provide a bare essentials starting point for new pool and spa owners to get started. If feels like a lot now but after a while you will find that almost all of the actual, day to day chemical corrections and water balancing you do will come down to maintaining proper chlorine levels in the water. Pool care does not have to be difficult! If you find you still need help and have questions you can always Ask Steve directly.


How To Fix Green Pool Water - See pool chemistry in action with this page on taking your pool water from green to clean




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Swimming Pool Steve is an award winning, second generation swimming pool specialist from Ontario Canada and one of the most trusted voices in the swimming pool industry. With over 20,000,000 views on the Swimming Pool Steve YouTube Channel, winner of the Pleatco Pool & Spa Industry Leadership award and author of hundreds of pool and spa articles both online and in print. Steve is committed to helping pool and spa owners as well as pool and spa industry workers learn more about the technical side of building, renovating, repairing and maintaining all types of swimming pools and spas. Follow Swimming Pool Steve on Facebook, Twitter and YouTube.


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