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Swimming Pool Chemistry Crash Course

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pool chemistry crash course
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.

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.

Can Pool Water Make You Sick?

While poorly treated pool or spa water can potentially kill bathers (or even people nearby and not in the water) fortunately this is fairly rare. Illnesses that confine you to your bathroom for a week wishing you were dead, or even worse in the hospital ICU for a spreading infection however, are more common. Most people do not eat chicken that has been in the fridge for five days because you can get sick. The reality is that most of the time you would not actually get sick...but you could. Swimming pool and hot tub water is the same thing. If you do not bother to balance your pool and spa chemicals then you are just eating five day old chicken hoping for the best.

Of all the chemicals that get used in swimming pools and hot tubs, the ones that are there to prevent bacteria growth and kill any potentially dangerous pathogens in the water are called chemical sanitizers. The most common of these chemical sanitizers are chlorine and bromine. When used correctly in a body of water they will completely prevent bacteria, viruses and pathogens from living, growing and multiplying. The only catch is they are not great for people and only in very small doses is it considered acceptable. This is why you do not simply add a wholesale amount of liquid chlorine to your pool once per year. The levels need to be monitored and maintained. There are also a small handfull of situations which can develop in the water where the chlorine that you use is unable to work properly such as when you hae high CYA levels (stabilizer) or if your pH gets above 8.0 where chlorine is almost completely not effective.

Basic Water Chemistry Values

Chlorine Total Alkalinity pH Calcium Hardness
1-5ppm (2-4ppm ideal) 60-180ppm (80-120ppm ideal) 7.2-7.8 (7.4-7.6 ideal) 150-1000ppm (200-400ppm ideal)

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. In the vast majority of cases when you have a problem developing with your water quality the answer to resolving the problem will likely be with one of these basic values being too far out of range. When you discuss problems with pool and spa water chemistry it is VERY important to use accurate terminology and numbers to describe your water condition. Your pool water is never "good". It is a series of specific numbers which you need to know to find the problem.

Additional Water Chemistry Values

Iron Copper Phosphates Cyanuric Acid
0ppm 0ppm 0ppm (500ppb maximum) 30-50ppm (80ppm maximum)

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. CYA, cyanuric acid or stabilizer is the sunscreen for your chlorine that prevents UV from the sun from destroying all of your chlorine every day. Over 80 ppm chlorine is mostly inactive, and over 100ppm the chlorine in the water is unable to function properly.

Chemical Sanitizers (Chlorine & Bromine)

Chemical sanitizers like chlorine and bromine are the primary line of defense against harmful pathogens that can grow in pool and spa water. In order to be considered a suitable chemical sanitizer the chemical must have four distinct properties:

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.

Do Pools Need Calcium?

Calcium hardness is the amount of dissolved calcium in the water (note: in this video I incorrectly state that CH is the amount of dissolved calcium and magnesium, however this would be total hardness). 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. 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.

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

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.

What is pool stabilizer?

Secrets to the best pool water

Alternatives to chlorine in pools

Why did my pool water turn green?

Is salt water bad for pools?

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