Chapter 3: WATER QUALITY. How to Build Your Own Home Swimming Pool or Spa

Chapter 3: WATER QUALITY. How to Build Your Own Home Swimming Pool or Spa

Water quality doesn't just refer to making your pool look pretty, all sparkling and blue in the summer sunlight.  It also refers to making sure that your pool is safe from disease, as well as free of unsightly and deadly algae.

It's a given that a pool needs to be disinfected.  Water is, after all, the source of life--and that isn't restricted to human life.  All animals love water, including insects and algae--and germs love water too.  Your swimming pool without regular disinfections is essentially a breeding ground for disease.

The problem, of course, is one of degree.  Disinfectants are poisons, after all, designed to kill unwanted life.  You probably don't define "unwanted life" as including "the friends and family members who use your pool."  So the key to maintaining your water quality is to keep the water filled with enough disinfectant to kill any unwanted organisms who use your pool as a convenient spawning ground, but not so much disinfectant that your pool becomes unsafe.

We can think of a pool as a sustained war between earth and water, as we said.  Think of your pool water as a sustained war between safe water and clean water.

Chlorine Pools

Chlorine is the oldest method of sanitizing public pools, and still one of the best.  If you're a first-time pool owner or if you just want to "get your feet wet" with pool maintenance, chlorine is most likely what you'll want to use.

The special chemical properties of chlorine make it ideal for use in swimming pools--as opposed to, say, muriatic acid or some other more frightening option.  Not that chlorine in and of itself isn't frightening--chlorine gas has long been a weapon used in modern warfare--but when mixed with water, chlorine has a history of doing the job you want it to do without "working overtime."

When chlorine tablets are added to pool water, two compounds are created: "free chlorine" and "combined chlorine."  Do the names sound too similar?  Think of them this way: free chlorine is "good chlorine."  Combined is "bad."

Why is free chlorine good and combined chlorine bad?  Simply: free chlorine is able to move freely around the pool, attacking and killing microorganisms.  Combined chlorine doesn't work effectively to kill microorganisms.  It just stays in the pool, floating around, producing unpleasant "pool smells" and bleaching people's hair and bathing suits.  Left unchecked, it can even eat away at the walls of a pool and cause maintenance nightmares.

You've probably seen or been in a pool with too much combined chlorine before.  The usual complaint from people is something like: "There's too much chlorine in this pool!  I can smell it!"  Surprisingly, the reason the pool smells like chlorine isn't because there's too much chlorine in the pool: there's actually too little, or at least too little that's doing the job it's supposed to do.

So the key to a good, workable pool is to keep the chlorine balance in your pool at the proper level.  We'll talk a little more about this later when we talk about the regular maintenance your pool needs.

Saline Pools

Saline pools are the most recent development in pool sanitizing systems.  Because they're so recent and because they're presented as an ideal alternative to traditional chlorine pools, you might be tempted to think that saline pools are some kind of radically different approach to pool maintenance.

But if you remember your high school chemistry, you'll remember that salt, chemically, is just sodium chloride: NaCl.  In other words, there's chlorine in it!  And that's all a saline pool is, essentially: an alternative method of delivering chlorine to your pool.

How does it work?  Simple.  The water is filled with salt to an acceptable level, usually around 3000 ppm (parts per million), although the exact amount depends on the pool's specific construction.  Two components are added into the pool's filtration system just after clean water passes through the filter: a control box and a "salt cell."

The control box is what you use to regulate the amount of chlorine fed into your pool.  By changing the time over which the salt cell is charged with electricity, you can change the rate of chlorine production and delivery.  There's no set formula for ideal chlorine production: either follow your pool installer's recommendations, or--if you've decided to install your pool yourself--maintain a chlorine level that keeps the water at an ideal pH balance.

When the control box is charging the salt cell, the salt cell converts the salt in the water into natural chlorine.  It does this through an electrolytic process.  The salt cell is filled with metal plates which carry alternating positive and negative charges.  When the cell is active, the water is electrified, which forces the salt in it to break down chemically into sodium deposits and natural chlorine.  The chlorine then flows back into the water through the returns.

You don't need to really know anything about how that chemical reaction works in order to maintain a saline pool: just know that salt water goes in, chlorinated water comes out.  But you've probably already spotted one maintenance issue with saline pools from that decision: where do the sodium deposits go?  The answer: more often than not, they adhere to the plates in the salt cell.  So every so often you'll need to take out your salt cell and clean the plates of any deposits.  Ideally, you can find a salt cell with a self-cleaning feature, which allows you to reverse the polarity on the water in order to shake the sodium deposits from the plates.  Again: there's no reason to know the chemistry behind it; just know that it needs to happen.

Alternative Water Disinfecting Methods

It's hard to beat chlorine, whatever the delivery method, when it comes to disinfecting and sanitizing a pool.  But in the words of Mr. Spock, there are always alternatives.

The most popular alternative disinfecting agent for a pool is bromine.  Bromine occupies the same chemical "niche" as chlorine and works in almost exactly the same way to clean a pool.  Due to its comparative rarity, however, (after all, you can get chlorine from salt!), bromine carries with it a much higher price tag and is sometimes hard to find in smaller towns. 

Despite the cost, bromine is actually preferred by some pool owners, and may be an option worth exploring if you have a non-saline pool.  The reason has to do with the chemistry of the water and how your disinfecting agents interact with it.

When you add chlorine to your pool, part of the chlorine breaks off to kill bacteria and other agents.  Once the good chlorine kills bacteria, it essentially vanishes and ceases to be effective.  The rest of the chlorine sits around, irritating people's skin and eyes and smelling up the pool until it's taken care of.  When bromine is added to the pool, all of the bromine is used in killing bacteria, since bromine is slightly more stable as a chemical than chlorine and isn't as likely to combine with other chemicals in your pool's water to cause unwanted compounds.  Once the filtration system removes all of the dead bacteria from the pool, the bromine is still active in the water and can be used to kill more bacteria.

In other words: bromine stays active in the water for longer.  Despite the higher price, a smaller amount of bromine can be used to do the same work as chlorine.  That's the great virtue of bromine--and also the great vice.

Since bromine and chlorine are so similar chemically, the human body often treats them in the same way when performing its own natural maintenance.  This means that if you're naturally allergic to chlorine, you'll usually be equally as allergic to bromine.  But since bromine is so stable compared to chlorine, it's very difficult to get bromine off of your body and clothes by washing them or taking a shower: the bromine tends to linger.  Since bromine doesn't smell or cause as much damage to the body as chlorine, many people don't find this to be a problem, but if you're physically sensitive to chlorine already, bromine is not a good alternative.  If you just don't like the smell of chlorine--and you don't mind the cost and availability issues--bromine may be your answer.