Aquatics & Recreation Specialist Guide: Chlorine in Commercial Pools

Andrew
Feb 27, 2018
6 min read

Contributor: Ivana Stojkovic

This is a basic introduction to Commercial Pool Chlorine with information intended for beginners with beneficial information for experienced operators. This guide talks primarily about chlorine as it is the most widely used sanitizer and oxidizer and will briefly discuss other non chlorine disinfectants.

Audience:

Property managers
Aquatics /Pool managers
Lifeguards
Waterpark staff
Recreation managers
Hotel managers
Maintenance / Facility employees

What you will learn:

What is a swimming pool Sanitizer/Oxidizer
How chlorine works
Chlorine and Water Balance
How Ph affects Chlorine effectiveness
How Cyanuric acid (Stabilizer) is hero and a villain in swimming pools
Which chlorine type is right for you
How do I add chlorine in my commercial pool?
Non Chlorine alternatives
Correct levels of chlorine
Testing for chlorine levels
Health departments rules in regards to chlorine
What to do if your chlorine level is low
What to do if your chlorine level is high
What is superchlorination (shocking)

TAKE THE QUIZ AND GET A CERTIFICATE OF COMPLETION

What is a pool Sanitizer/Oxidizer?

In relation to usage for commercial pools, chlorine is a very effective, (and one of the few to both be a) Sanitiser and Oxidizer.

It Sanitizes (Deactivates/Kills) 99% of bacteria and viruses within a few seconds/minutes and Oxidation is the breakdown by burning of organic molecules that transform safely to gas and leave the pool. For example, algae, sweat, leaves and fecal matter.

How does chlorine work?

When chlorine is added to water it produces hypochlorous acid which is the actual sanitation and oxidizing agent. How much of this is created, will be dependent on water temperature and especially the water pH level.

Hypochlorous acid or free chlorine is the part of the total chlorine that has not reacted with contaminants, and is "free" to go to kill bacteria and other contaminants. Only the chlorine in this form is capable to sanitize.

Free chlorine or hypochlorous acid tends to be unstable in the presence of sunlight and high temperatures which causes rapid chlorine loss in pool water.

For example, a gallon of chlorine, after one hour of exposure to UV light, is only approx 60% effective as a Sanitiser/Oxidizer

Chlorine and water balance

While chlorine in small amounts does not have a large effect on water balance it does have an effect on Ph depending on what type of chlorine you use. For Example, bleach (Sodium Hypochlorite) will raise Ph making chlorine less effective, while stabilized chlorine (Trichlor) will lower.

How does Ph affect the effectiveness of chlorine

As the Ph level goes up the effectiveness of Chlorine goes down.

Chlorine is more effective in lower Ph conditions e.g. 7.2 and less effective at 7.8.

This is why the ideal pH range of 7.4-7.6 is recommended in addition to neutral effects on human skin and eyes.

How Cyanuric acid (Stabilizer) is a hero and a villain in swimming pools

Cyanuric acid is used as a chlorine stabilizer in swimming pools and has been used in pools for at least 50 years. It binds to free chlorine and releases it slowly, extending the lifetime of chlorine when exposed to UV rays.

The common analogy for stabilizer is that it acts as ‘sunblock’ for chlorine, protecting it from UV rays which destroy chlorine before it can act as a Sanitizer/Oxidizer.

It is highly recommended to use stabilizer to make your chlorine last longer in a commercial swimming pool, however ‘more is definitely not better’. When stabilizer levels are high then more chlorine is needed to do its job , thus offsetting the savings spent on more chlorine

Health departments generally allow stabilizer levels as high as 40-100 ppm depending on a spa or pool. However at these higher levels the ‘killing’ power of chlorine is slowed down so much that it can't eliminate enough bacteria or algae fast enough and it is not unusual for algae to grow even while chlorine levels are high.

In addition, high stabilizer levels should be taken into account when determining pool closure time due to a fecal accident.

In summary stabilizer is both the cure and the poison at low and high doses so it is recommended to keep CYA/Stabilizer levels between 20-30 ppm.

The graph above shows that stabilizer is 95-98% effective in protecting chlorine at 20-30 ppm as it is at 40+ levels of stabilizer.

Which chlorine type is right for you

This will depend on several factors and not always lowest price. Such as,

The size in gallons of your pool.
The training and experience level of your pool operator
The usage of your pool. E.g. a large city waterpark compared to a homeowners association pool.
Availability of chlorine types in your area
Safe handling requirements such as a dry compound over liquid
Is the pool indoors or outdoors
Whether you have room for large bleach containers or small tablet feeders
Whether your chemical area is fenced off or not

*Safety considerations- relative to use of safety Training, Equipment and Procedures

**Cost - depending on size of pool in gallons/availability/chlorine demand

What is free available chlorine?

Total chlorine - is the sum of the free available FAC chlorine and combined chlorine in water.
Free available chlorine (FAC) or hypochlorous acid.
Combined available chlorine (CAC) or chloramines - is the part of total chlorine in the water that has reacted and combined with contaminants such as perspiration, urine, swimmer waste, ammonia. Some chloramines can cause eye irritation and chlorine odors.

Always take the proper precaution in dealing with pool chlorine. Remember to read the manufacturer's labels.

Chlorine residual and Chlorine demand

Since Free chlorine is constantly sanitizing and oxidizing it is important to keep a minimum RESIDUAL at all times. All swimming pools can develop "CHLORINE DEMAND" when insufficient chlorine is present. Dissolved iron, bacteria, perspiration, algae, pollen spores, and other organic materials create a "CHLORINE DEMAND" in pool water.

If enough chlorine were continuously added to form an ideal amount to sanitize/oxidize all of the pollutants present, a "CHLORINE DEMAND" would no longer exist.

Testing for Free and combined chlorine levels in pool

How do I add chlorine in my commercial pool?

This will depend on the type of chlorine you decide is best for you!

However, in a commercial pool with various liability issues it is important to use a consistent method of adding chlorine. Most Health Departments require a ’disinfection feeder or generator’

THIS EQUIPMENT REQUIREMENT EXCLUDES THE ADDITION OF CHLORINE DIRECTLY INTO THE POOL AS YOUR ONLY/PRIMARY METHOD OF CHLORINE DELIVERY.

If you do add chlorine directly into the pool to supplement chlorine feeders then there must be no swimmers present during and for at least an hour after addition

Most commonly used forms of chlorine feeders:

Peristaltic pumps - these pumps pull liquid chlorine from a container in a similar way humans swallow liquids with the contraction of tubing. This tubing then directly inserts the chlorine into the piping flow back into the pool. Chlorine addition can be increased or decreased with speed or larger tubing size.

Tablet Erosion feeders - tablets of dry chlorine are placed in the container with water flow going thru the feeder and back to the pool. The tablets are ‘eroded’ by water flow and chlorine addition can be increased or decreased by adjusting the flow. The correct type of erosion feeder should be used for Cal Hypo or TRi Chlor. It is not advised to place chlorine tablets in a commercial pool skimmer baskets as swimmers especially small children may come in direct contact and cause illness or injury.

Salt chlorine generators - a generator is installed in the pool piping and when pool water that contains salt passes thru an electrical charge it changes the chloride ions into chlorine gas which dissolves and continues back to the pool.

What level should chlorine be in the pool?

Some states have different minimum and maximum allowable values

How do I lower chlorine in the pool?

Ideally, just turn off your chlorine feeder or stop adding chlorine until it comes within the ideal range of 2-5 ppm. This may take days depending on usage.

The following are ways to reduce chlorine,

Let UV rays deplete the chlorine
Partially Drain and refill the pool
Use Sodium Thiosulfate to reduce chlorine in a much shorter time.

What is breakpoint superchlorination (shocking)

Besides normal residual chlorination, chlorine is also used to shock or super chlorinate pool water, in order to remove all unwanted compounds from the water, to destroy impurities like waste products and algae, and break apart the chemical bond of chlorine combined.

The point at which the chlorine concentration is high enough for these chemical bonds to be broken is called BREAKPOINT.

Break-point chlorination eliminates chloramines and other reactants which cause an increased chlorine demand.

TAKE THE QUIZ AND GET A CERTIFICATE OF COMPLETION

Non chlorine options CLICK THE IMAGE