Max
Combined Chlorine
There is some controversy over what is an “acceptable” combined chlorine level.
Some experts and NSPI (National Spa & Pool Institute) say that combined
chlorine should not be more than 0.2 ppm in public or
commercial pools. Others say that combined chlorine should not be more than 20%
of the FAC. (Free Available Chlorine) (I think this 20 percent idea was a
result of saying the 0.2 ppm combined chlorine is 20
percent of the often required minimum of 1.0 ppm
FAC). Local health departments and State health codes are the ultimate
jurisdiction for a given commercial or public pool or spa. Check with your
local authority.
Superchlorination To The Rescue
Suppose you superchlorinate by raising the FAC to 10 ppm, holding it for four hours and the next day the
combined chlorine reading is back up to 0.8 ppm or
higher. Then you try adding a non-chlorine shock. Many hours later or the next
day your combined chlorine residual is back (or correctly, your nuisance
residual is still there).
A level of 0.2 ppm of combined chlorine in your pool
is unacceptable for a number of reasons.
First, if the combined chlorine is comprised of mostly chloramines, then you
will have eye and skin irritation and a very pungent, noticeable “chlorine”
smell around the pool. Want proof?
Here it is:
Chloramine Taste and Odor Threshold
Type pH Taste Odor
Monochloramine ( )
8 – 9 0.48 ppm 0.65 ppm
Dichloramine
( )
4.0 0.13 ppm 0.15 ppm
Nitrogen Trichloride ( )
0.02 ppm 0.02 ppm
Source: Aroma and Flavor Characteristics of Free Chlorine and Chloramines. In
Proceedings of 12th Annual AWWA WQTC, 1984,
Accurate Testing Critical
Manual water tests using a test kit capable of distinguishing between free and
total chlorine should be performed by the pool operator every two hours. (Many
States have regulations that require water testing three times per day or even
once per hour during hours of operation if it is a busy commercial or public
pool or spa.)
Determining the amount of combined chlorine is critical to successful
commercial or public pool and spa operation.
The traditional method of determining combined chlorine is to make a free
chlorine test and a total chlorine test and then subtract free from total. The
difference between free and total is combined chlorine.
Test Kit Drawbacks
Unfortunately the most common chlorine test kits have some serious drawbacks
for making a determination of combined chlorine.
First, DPD free and total chlorine tests are colorimetric meaning that you must
determine concentration from distinguishing various shades of pink to red to
get each reading. You must make a test for free and a second test for total
chlorine. You have two chances to make an incorrect determination of color. And
then you subtract one from the other.
Second, the increments or graduations for determining the free or total
chlorine concentration are usually 0.0, 0.5, 1.0, 1.5, and so on. You need more
accuracy than that. The NSPI guideline and most Health department regulations
want the combined chlorine level to be 0.2 ppm or
lower. It is very hard to tell any level of chlorine between 0.0 and 0.5 ppm (let alone a level of 0.2 ppm)
with a traditional DPD colorimetric test.
What’s New?
There is a relatively new test kit that has made life a little easier for
determining free and combined chlorine. It measures free chlorine and combined
directly – you don’t have to subtract free from total because it reads combined
directly. The test kit is called an FAS DPD test kit. It is a titration type of
test rather than a colorimetric type of test. This is the type of test where
you get a water sample, add a reagent, a color develops, and you add another
reagent drop-by-drop mixing between drops until the color changes or goes away.
The number of drops used to reach the change (called the end point) multiplied
times a factor equals the concentration. With the FAS DPD test a drop is equal
to either 0.2 ppm or 0.5 ppm
of free chlorine or combined chlorine depending on water sample size and
whether you use the free or combined reagent. The water sample turns pink when
free chlorine or combined chlorine is present and you add drops until the color
goes from pink to clear. It is much more accurate than the old color match test
kits and it is even ideal for people that are color blind. Many people are
color blind to the pink to red colors developed with traditional DPD reagents.
Reaching the Breaking Point
They way to get rid of these chloramines is to
increase the ratio of chlorine to ammonia to 7.6 to 1 or higher. If you don’t
attain the ratio of 7.6 to 1 or higher, you do not destroy the ammonia. Once
the ratio is attained, all ammonia will be destroyed. However, if you made a
slight mistake in the test kit evaluation or you multiplied incorrectly, you
may add the wrong amount of chlorine to the water to destroy the ammonia. Also,
if you added exactly the 7.6 to 1 amount, you would have no chlorine residual
left in the water. Therefore, it is common practice in the pool and spa
industry to multiply the combined chlorine reading by 10 and add that amount to
the water in one mega-dose. This will ensure that the chloramines are destroyed
and there will be a residual when the chloramines are gone. This process is
called breakpoint chlorination. You have reached breakpoint when you have
destroyed all the chloramines.
Multiply Times 10
As I said, you don’t want to waste chlorine or money
so you want to add 10 times the combined chlorine level. Because you are
multiplying 10 and adding it the water, it is much easier and cheaper to
monitor and add the chlorine when the chloramine
level is small or low.
If the chloramine level in your pool is 0.2 ppm, all you have to do is add 2.0 ppm
of free available chlorine to the pool and they will be destroyed. If you are
using an automatic chlorine controller, all you need to do is raise the
chlorine level by 2.0 ppm in addition to the level
you are maintaining and they chloramines will be destroyed.
As an example, suppose you are keeping a chlorine level of 1.5 ppm of FAC in your pool. You notice that the chloramines
level has gone to 0.2 ppm. All you do is set the
controller to raise the chlorine level to 3.5 ppm and
the chloramines will be destroyed (0.2 × 10 = 2.0 then 2.0 + 1.5 = 3.5). You
can add this amount to the water and the swimmers will never know it.
The
Another method of ridding the water of ammonia and chloramines is to try using
a non-chlorine shock such as potassium peroxymonosulfate
(often called monopersulfate or MPS). Other
non-chlorine shocks are sodium persulfate, sodium percarbonate or hydrogen peroxide. Be aware that the last
two will dechlorinate the water.
Dry, non-chlorine shock treatments are used at the rate of one pound for each
10,000 gallons of water. This dose level will remove about 1.0 ppm of combined chlorine or ammonia. If your combined
chlorine level is higher than 1.0 ppm, you should add
a larger dose. Again, if the combined chlorine level comes right back, you may
have to shock more often.
Be aware that non-chlorine shock will react with the DPD reagent and can give
you a false reading on your free and total test kits. Some test kit
manufacturers have test kits for non-chlorine shock and some have additives to
neutralize the non-chlorine shock before making the free or total test.
Prevention Is Key
Most people use non-chlorine shock after they develop chloramines just like we
do for superchlorination. However, many pools are now
adding non-chlorine shock before they develop chloramines or combined chlorine.
Again, testing is the key. If you are developing 0.2 ppm
of combined chlorine every day in your pool, you may be able to add enough
non-chlorine shock to knock out the ammonia before it combines with the
chlorine in the water. If one pound of non-chlorine shock will destroy one ppm of ammonia, then 0.2 ppm of
ammonia will require about 3-4 ounces of non-chlorine shock. You could just
start adding about 3-4 ounces of non-chlorine shock every day to take care of
the ammonia as it is introduced.
Another way to accomplish this is by using a test strip that measures monopersulfate (MPS) in the water. You can establish a
residual of MPS in the water to take care of any ammonia. MPS test strip are
available now.
If All Else Fails
If not there are only a few things left to try.
You Need Less Bathers
You could restrict the number of bathers or require that they shower before
entering. A smaller bather load will decrease the swimmer waste that creates
the combined chlorine.
Shower Before Entering
You can also enforce a shower-before-entering
requirement. Rinsing off the bacteria, suntan lotion, soap, oil, deodorant,
hair spray, makeup, and other personal care creams and lotions will
significantly cut down on the pollution that causes combined and nuisance
residuals.
Draining May Help
You could drain and replace more water more often in the pool. The European
standard (called the DIN Standard) requires water replacement of 30 liters
(about 8 gallons) of water per swimmer per day. If you had a daily bather load
of 400 people then you would need to drain off 3,200 gallons of water per day
and replace it with fresh water.
Get Excited About Ozone
You could use ozone as a secondary oxidizer or even as
a primary oxidizer with either chlorine or bromine. Most public, commercial,
large pools are on a budget so switching over to ozone may be too expensive
(about $10,000 to $50,000).
To use ozone as a primary disinfectant requires a large corona discharge (CD)
ozone unit to disinfect the main flow of water. Then a residual of chlorine or
bromine is required because ozone does not provide a lasting, measurable
residual in the water.
To use ozone as a secondary disinfectant requires a much smaller ozone unit
that injects the ozone in part of the main flow of water (called a side
stream). This side stream is usually about 20-25 percent of the main flow.
After injection with ozone, the ozone-treated water returned to and mixed in
with the main water flow back to the pool. In this way, chlorine is still the
primary disinfectant and ozone is there to work on the swimmer waste and
ammonia that cause combined chlorine.
UV You See
Ultra Violet (UV) light may help. You are probably aware that sunlight (UV
rays) is chlorine’s biggest enemy. It will destroy 90 percent of free chlorine
in just two hours in direct, summer-time sunlight. We use cyanuric
acid (called stabilizer, conditioner or CYA) to slow down this UV degradation.
Chlorine stays around 8-10 times longer with cyanuric
acid in the water. Well, UV also will destroy combined chlorine. Because there
is so little UV light in an indoor pool, you may need to install a separate,
special UV light chamber in the plumbing line to destroy the chloramines. This
works very well. However, be aware that this strong intensity UV light will
also destroy some of the free chlorine too.
Try A Carbon Copy
You could also use a carbon or charcoal filter. However, it is expensive and in
addition to removing the chloramines, it will dechlorinate
the water and remove the cyanuric acid. Chances are
that the carbon will load up with cyanuric acid long
before it removes all the chloramines. Regeneration or replacement is expensive
too.
Get Rid of The Chlorine
The same chemicals that remove chlorine (anti-chlor, dechlor, chlorine neutralizer) will also remove chloramine and combined chlorine. Of course these chemicals
are fairly expensive and you already bought the chlorine in the water. Using
chlorine neutralizer will take all of the chlorine residual out of water and
then start working on the combined chlorine. Then you have to buy the chlorine
to establish a new chlorine residual in the water. So you get to pay three
times – one for the original chlorine, two for the neutralizer and three for
the new chlorine residual.
The following chemicals are used as chlorine neutralizers: Ascorbic acid,
Calcium thiosulfate, Hydrogen peroxide, Oxalic acid,
Sodium ascorbate, Sodium bisulfite,
Sodium metabisulfite, Sodium sulfite, Sodium thiosulfate and Sulfur dioxide.
However, this method is fast and certain. You must be careful to get enough
chlorine neutralizer in the water to completely wipe
out all chlorine residual plus any combined chlorine. Testing is critical.
Over-dosing is OK but it is expensive because any extra neutralizer left in the
water will destroy any new chlorine added until the neutralizer is all used up.
Adding too little and you don’t get rid of the combined chlorine. Also, this
method does not remove free ammonia in the water.
What’s A Zeolite?
Zeolite is a natural, safe and clean, easy care
alternative to the #20 grade silica sand used in sand filters.
Millions of years ago, zeolite deposits formed when
volcanoes erupted large amounts of ash. Some of the
wind-borne ash settled to form thick ash beds. In some cases, the ash fell into
lakes and oceans. When volcanic ash falls into salt water, a chemical reaction
takes place that produces zeolite – technically
hydrated aluminosilicates of alkaline earths. The
differences in location such as temperature, salt content, sunlight and a few
other properties make each zeolite deposit slightly
different. For example, clinoptilolite has a natural
ratio of silica to alumina of 5 to 1 while chabizle
has a ratio of 2 to 1.
Clinoptilolite’s (called clino)
unique crystalline structure and chemical properties make it an excellent
replacement for sand as a filter medium. It has a huge surface area and it has
natural water softening properties through ion exchange.
Zeolite has a unique ability to absorb ammonia and
chloramines. Ammonia enters the water from swimmer sweat and urine. Through an
ion exchange capability, zeolite can absorb ammonia
and release its sodium into the water. Of course once it has reached its
capacity to hold ammonia, it must be recharged.
To recharge the ammonia removing capabilities, you mix up a 10 percent salt
solution (1 oz. of salt to 10 fluid oz. of water) and pour it into the zeolite in the filter. Let this sit for 10 – 12 hours and
then backwash to waste.
The Worst Thing You Can Do About Chloramine
and Nuisance Combined Chlorine is Nothing
Doing nothing about a nuisance or combined chlorine problem may be too
expensive.
If All Else Fails
A nuisance residual that will not go away even if you tried every suggestion
above is a problem. The only thing that can be done is to drain most of the
water and start over. Sorry but this is sometimes the only thing that works.
Next time handle it before it gets to be a nuisance.