Swimming Pool and Spa Water Chemistry

Swimming Pool and Spa Water Chemistry

Missouri Department of Health and Senior Services Section for Environmental Public Health

Table of Contents

Water Sanitizing Components Chlorination Sanitation Oxidation Superchlorination Combined chlorine Breakpoint chlorination Inorganic and Organic Chlorine Effect of pH on Chlorine Chlorine Gas Sodium Hypochlorite Calcium Hypochlorite Lithium Hypochlorite Lithium Hypochlorite Chlorinated Isocyanurates Chlorination Summary Alternative Sanitizers Bromine Iodine Ozone Electrolytic Cells Brine Method In-Line Method Automation Silver Non-Chlorine -Oxidizers Other Pool Chemicals Flocculants Algaecides Chelating or Sequestering Agents Degreasers Defoamers Cyanuric Acid

Balanced Water Chloride Bromide pH Total Alkalinity Total Hardness Total Dissolved Solids Stabilizer

Pool and Spa Water Testing and Testing Routines Chlorine Bromine pH Total Alkalinity Total Hardness Total Dissolved Solids Superchlorination or Shocking

Adding Chemicals to Water Glossary of Terms ? Water chemistry Troubleshooting Guide

Pool Spa Advanced Pool and Spa Water Chemistry

Chloramines OTO DPD

General

On a hot summer day, who wouldn't want to jump into a cool and refreshing pool? And then, as the sun sets, what better way to relax than to slip into your own backyard spa -summer or winter?

But enjoying all that requires some regular attention. Remember, the water in your pool and spa is an ever-changing environment that calls for constant and careful monitoring. For some, this means hiring a professional service technician to come by once or twice a week. You can, however, take care of your pool and spa yourself.

The need to treat water has been widely accepted for a long time. Sanitation, especially, is recognized as a means of controlling communicable diseases. The pool operator is expected to provide safe, clean water for bathers.

More recently, however, the importance of mineral saturation, or 'water balance" as it is more popularly known, is recognized by those responsible for maintaining the pool and equipment. Water can become aggressive and destroy pools with corrosion, or it can become scaling and damage the pool with mineral deposits.

The pool operator must learn about the use of chemical agents for sanitation and for control of pH, total alkalinity and calcium hardness. The operator is expected to protect both the swimmers and the pool itself. This chapter is written to present the necessary chemical treatments and sufficient background information to know when and how to use them.

Here's a basic guide to pool and spa water chemistry. It will give you a general outline of the issues that shape routine care.

Water Sanitizing Components

As you probably know, the occasional addition of new water -- or wholesale water replacement in the case of spas -- isn't enough to keep the water clean and clear of unwanted and often microscopic contaminants.

But worry not! Pool and spa chemists have spent years developing a variety of tests and chemical-treatment methods to keep your pool and spa safe and sparkling clean.

Your goals here are water sanitation and water balance. In other words, you want your levels of sanitizers (such as chlorine or bromine) and your levels of pH, total alkalinity, water hardness and total dissolved solids to all fall within acceptable limits.

And learning to keep these areas in check isn't as complicated as it may seem. To simplify things, we'll explain the relevant topics one at a time.

Sanitizers Bromine Chlorine

Sanitizers, or disinfectants, are hardworking chemicals. They also have a killing streak in them -- which is exactly what you want.

The important thing to keep in mind is, that for them to do their duty, they have to be present in the pool and spa water at all times. There always needs to be a certain minimum amount -- called a residual -- of sanitizer in your water.

What we're saying is, to make sure your pool and spa are protected from bacteria and their friends, you need your sanitizers on 'round-the-clock duty.

When you add your sanitizer, therefore, you should be adding enough to kill any existing contaminants in the water -- and create a residual that can neutralize any dirt, debris or germs that may get into the water before you next treat it.

That said; let's take a look at some of the most common sanitizing chemicals and equipment available on the market today.

Also available on the market today is a chemical sanitizer called bromine. Do note, however, that bromine cannot be stabilized with cyanuric acid. As much as 65 percent of bromine residual can be depleted by the sun in a two-hour time period. Because there is no known way to retain a reliable level of bromine when exposed to sunlight, many experts recommend it for indoor pools or spas only.

FYI: The acceptable range of bromine for your pool or spa is from 2.0 to 4.0 ppm.

Bromine also has no odor, and dispensing it your spa via a feeder allows it to dissolve at a slow, constant, desirable rate. Just be sure to remove the feeder when your spa is in use.

A final note: When using bromine as your sanitizer, you will need to occasionally shock the water with large doses of another chemical to oxidize waste material still in the water. (We'll explain this in more detail below.)

Chlorine has been somewhat of a wonder drug for pool and spa environments. It has the power to kill bacteria and algae -- and works extremely well in aqueous environments.

Chlorine is not invincible, however. Like most chemicals, it has a threshold -- a point at which it has used up all its sanitizing power and can no longer protect your pool and spa water.

Chlorine levels are also heavily influenced by evaporation, splash out and destructive UV rays, not to mention a low pH. (You'll read about this last factor in more detail below.)

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