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There are two well-known test
kits available to test levels of chlorine and bromine, the DPD and
OTO. Each has a long, scientific name, but all you really need to
know are the initials. The DPD is the preferred of the two because
it tests for free available chlorine -- the most powerful
"killing form" of chlorine. Its chemical reagent reacts
with the free available chlorine in the sample water to change its
color. The ideal range of 1.0 to 3.0 ppm for pools or 1.5 to 3.0 ppm
for spas will command a pink to red color. To get an accurate
reading, just compare your test sample to the manufacturer's chart
that should be included with the test kit.
Note: An extremely high level
of chlorine tends to bleach out the test water, making it appear as
if there isn't any chlorine present. This would normally prompt you
to add more chlorine, and in most cases, that's correct. If you
think you have received a false reading, conduct the test again,
except this time, fill the test vial with 50 percent chlorine-free
or tap water and multiply the results by two. This will help you
determine whether you have a low level or very high level of
chlorine in your water.
The other, less common, test
is the OTO, which works on the same basic principle, but will turn
the water yellow to deep orange when chlorine is in the proper
range. One of the major differences between the OTO test and the DPD
test is that OTO cannot distinguish between total chlorine and free
available chlorine. You won't get an accurate estimate of how much
killing chlorine is in your pool or spa water. A final note: Bromine
can also be tested using either method, but the results need to be
multiplied by 2.25 to yield a true reading - - unless, of course,
you have one of the test kits that include a bromine color chart as
a reference. So far so good? Let's move on to pH.
The most common pH test for
pool and spa owners is the phenol-red test. Just like the DPD and
the OTO, the phenol-red test has a reagent that mixes with the acid
in the water to cause a color change in the sample. If your pH is in
the correct range, the water sample should turn a shade of red
ranging from pink to orange. If you get a yellow result, you have a
low pH or acidic water. If the color is a deep purple, your pH is
too high. Once again, you'll need to compare your results with the
color chart provided with the test kit to get an accurate reading.
TESTING
FOR pH VALUES
pH of water is determined by adding a reagent
(containing an organic dye) to the sample at a measured rate.
Reagents to cover the entire pH range of 1.0 to 14.0 are available.
Because most pools are kept in a pH range of 7.2-7.6, the pH test
that uses phenol red as a reagent is particularly effective (pH
range of 6.8-8.2). Phenol red is available in either liquid or
tablet form. To test with phenol red, add one tablet or a specified
number of drops of liquid, to the water sample, and compare the
resulting color to the test-kit standard. At the low end, the sample
is yellow, developing an increasingly red color as the pH increases.
At the high end, the color is almost purple.
Some reagents are subject to bleaching by
chlorine; others react with the chlorine to form new compounds that
can give false readings. Bleaching action should be neutralized by
adding a 2-4 drops of chlorine neutralizer (sodium thiosulfate)
before the test is performed. (Some indicator solutions sold
specifically for pools already contain a chlorine neutralizer to
combat this bleaching action.)
Solution
Method for Testing for pH Value
- Rinse the sample cell in pool water.
- Fill the sample cell to the marked fill
line with pool water.
- Add 2-4 drops of chlorine neutralizer to
remove the chlorine and prevent bleaching. (As mentioned
earlier, many test kit manufacturers market pH indicators
containing chemicals that eliminate the bleaching effect of
chlorine, making this step unnecessary.)
- Add the prescribed number of drops of
phenol red to the sample cell.
- Cap the sample cell, and mix the contents
by inverting several times, or swirl. Do not use a finger in
contact with the solution.
- Compare the color of the sample with the
test-kit color standards.
Look for a hue or color comparison, not a
color intensity, as in the chlorine test. A shade between two
standard color values indicates that the pH is the midpoint between
the values assigned.
Tablet
Method for Testing for pH Level
- Rinse the sample cell in pool water.
- Fill the sample cell to the marked fill
line with pool water.
- Add one phenol red indicator tablet to the
cell. Invert the sample cell to dissolve the tablet.
CAUTION: Do not
shake the solution vigorously. If the tablet fails to dissolve with
gentle agitation, crush it with a clean plastic rod.
After the tablet has dissolved, compare the
color with the standards, as above.
Note: The spa's temperature
makes a definite impact on the accuracy of this test. Therefore, the
test should only be conducted with spa water when its non operating
temperature is between 60 and 80 degrees Fahrenheit. Adjusting pH is
a very simple task. If you have a low pH, add soda ash or sodium
bicarbonate. If your water's pH is high, add liquid muriatic acid or
dry acid. (Remember, both soda ash and muriatic acid are too strong
for use in spas.) Before you attempt to change the pH, however, you
need to perform a second test to figure out how much of which
substance you'll need to add to the water. A base-demand test
determines how much soda ash or bicarb is required and an
acid-demand test calculates how much muriatic or dry acid is needed.
These tests are called titration tests or end-point reactions. In
this type, the number of drops of a special liquid it takes to cause
a color change corresponds with the amount of soda ash or acid
required. Consult the test kit manufacturer's recommendations for
the exact amounts. One more caution: Before doing anything about
your pH levels, you also need to test the total alkalinity of your
pool or spa water, as described below.
This test -- the last of the
regularly performed tests -- measures total alkalinity. As noted
above, this test should be done before you do your pH test and
adjustments. The two factors are interrelated and must be dealt with
together. Total alkalinity is determined by using a titration test
with two reagents. The first changes the color of the test sample,
the second triggers an end-point reaction. It's with the second test
you count the number of drops of reagent added to the water --
swirling the sample after each drop -- until it changes color. Note:
This reaction occurs very suddenly so don't add the second reagent
too quickly.
TESTING
FOR TOTAL ALKALINITY
Take a 100ml pool water sample in
a stoppered bottle. Using Palintest Alkalinity M tablets, add one
tablet at a time shaking the bottle until dissolved. Keep adding
tablets until the color changes from yellow to bright pink. Count
the number of tablets used and work out the alkalinity - Alkalinity
= (number of tablets x 40) - 20 ppm.
Testing for total alkalinity is essential to
make proper determinations of the saturation index as well as for
bather comfort and ease of pH control.
A pool's total alkalinity may be determined
through use of one of many commercially available test kits. A
quantity of pool water is mixed with an indicator; a blue color
reveals the presence of alkalinity. A reagent is added to this
mixture from a dropper. The operator counts the number of drops
necessary to neutralize the alkalinity and bring about a color
change. Alkalinity can be determined by multiplying the number of
drops used by a constant as provided by the test kit manufacturer
(usually 1 drop = 10 ppm).
Tablet methods also are available for
determining alkalinity. Although less accurate than the drop
counting method, the process is easy to follow and is less
susceptible to operator error. Tablets are added one at a time until
the desired color change takes place. When sufficient tablets have
been added to bring about the end-point color change, the number of
tablets required is multiplied by the constant provided by the
test-kit manufacturer.
It is recommended that the results of total
alkalinity be considered before adjusting pH. The direction of pH
change, or even the need for adding chemicals, is greatly influenced
by the level of total alkalinity. Total alkalinity does not vary
quickly and often is only tested once a week.
Calcium
Hardness Levels
Tests for calcium hardness are
performed at the beginning of the swim season, when you start up a
new pool or after draining and refilling a pool or spa. After that,
they only need to be done every three months or so. But don't forget
about it entirely because when allowed to go too high or too low,
the water's hardness levels can cause all kinds of problems. (For
more on water hardness, see the section on Keeping Your Water
Balanced.) Like total alkalinity, an end-point reaction best
measures calcium hardness. The first reagent is a pH buffer to bring
the pH level up to approximately 10. The second step adds a dye
that, when reacting with calcium, turns the sample water a different
color. Next, the titrant (EDTA) is added one drop at a time until
the water changes color. The total number of drops required gives
you the amount of hardness when compared with a manufacturer's
chart.
TESTING
FOR CALCIUM HARDNESS
Take a 100ml pool water sample in a stoppered
bottle. Using Palintest Calcium Hardness tablets, add one tablet at
a time shaking the bottle until dissolved. Keep adding tablets until
the color changes from pink to bright violet. Count the number of
tablets used and work out the hardness - Hardness = (number of
tablets x 20) - 10 ppm.
Calcium hardness in a freshly filled pool can
be approximated by taking 70% of the total hardness level. However,
more accurate measurements can be made by using a test kit designed
specifically to determine calcium hardness and by following the
manufacturer's directions regarding color changes.
In these tests, a specific amount of water is
taken from the pool, and an indicator is added to the sample. A
reagent is added, causing a color change that indicates the calcium
hardness level in ppm.
TESTING FOR TOTAL HARDNESS
To test for total hardness, an exact amount of
pool water (usually 60 ml) is treated with a solution called a
buffer. Then a dye is added. The reagent is added to the sample and
mixed, one drop at a time. The number of drops necessary to change
the water color, multiplied by a constant provided by the
manufacturer, determines the hardness in ppm.
The tablet method for testing water hardness
is equally simple. A tablet containing the pH buffer, the indicator
dye, and the hardness reagent is added to a 100 ml sample of water.
The color changes as additional tablets are added. The number of
tablets required to bring about this change is recorded and
multiplied by a constant provided by the test-kit manufacturer.
TESTING FOR TOTAL DISSOLVED
SOLIDS
Total dissolved solids (TDS) is the
measurement of all materials dissolved in the water, i.e., calcium,
carbonates, dissolved organic and inorganic materials, salts from
chlorine residue, swimmer waste, soluble hair and body lotion or
anything placed in the pool that can be dissolved.
TDS is measured by using a portable electronic
analyzer. The equipment is specifically used to measure for
dissolved solids and should be standard equipment for operation of
spas and hot-water pools. A pool should be dumped and refilled when
a TDS reading exceeds 1,500 ppm above the domestic water supply
reading. This equipment is quite expensive and is not normally at
the disposal of the private pool owner, so you have two choices:
- Take your sample of pool water to your pool
center and ask them to measure TDS for you. They will normally
be happy to do this for you free of charge if you usually buy
your chemicals etc from them.
- As TDS plays a less important part in the
calculation than the other factors you can estimate it, but do
bear in mind that this will then only give you a rough idea of
whether the water is scale forming or corrosive. As a guide, for
pools which have been recently refilled, use a figure of 750ppm.
For pools which have not been recently refilled, or where there
has been little water replacement by backwashing, or where
cyanuric acid levels are above 200ppm, use a figure of 1500ppm
for TDS.
Super chlorination is a term
that describes an extra large dose (usually 8 to 10 ppm) of chlorine
to oxidize organic compounds and kill and remove algae and other
contaminants from the water. This is the same as using three to six
times the normal dosage of a chlorinating agent. For example, a
50,000-gallon pool requires about four gallons of liquid pool
chlorine (12% Available Chlorine) or six pounds of a granular
chlorinating compound such as calcium bypochlorite (65% Available
Chlorine).
As mentioned, HOCI is the form
of chlorine that provides sanitation. Because it is an extremely
active chemical, however, it also reacts with organic impurities.
When there is enough HOCI present, the impurities are completely
oxidized. Combined chlorine is formed when there is an insufficient
supply of HOCI or when there is a very high level of organic
impurities. Combined chlorine compounds can be oxidized by
increasing the HOCI level in the water. The point at which all the
organic impurities are oxidized is called the breakpoint. The
addition of sufficient chlorine to reach this point is known as
breakpoint chlorination.
Every once in a while, your
pool or spa water may become a veritable hotel of unwelcome
contaminants and bather waste products. You can often detect when
this happens because a "chlorine" odor may begin emanating
from your pool or spa, or you may notice that you're experiencing
some skin and eye irritation. But the most reliable -- and better --
way to monitor your water quality is to take a second look at your
sanitizer readings. If your chlorine test readings keep dropping
hard and fast, you may be faced with the need to evict chloramines
from the water. (For more on how chloramines form, see the section
on Keeping Your Water Balanced.) This is done easily enough with a
process called shocking. No, you don't electrocute the chloramines.
What this process entails is adding extra high doses of sanitizers
to the water. By adding a large dose of chlorine -- a process called
super chlorination or shocking -- you bring up your residual of free
available sanitizer in a relatively short period of time. The newly
added sanitizer will promptly rid your pool and spa water of those
annoying guests. To be safe, do not use your pool or spa for at
least 24 hours after shocking with chlorine. You should also test
for the proper sanitizer levels before getting back in the water.
Note: There are non chlorine
shocking products available that lessen the amount of time swimmers
need to stay out of the pool or spa. Check with your local pool/spa
supply store or professional service technician for more
information.
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Add large amounts gradually
in thirds over a 2-hour period.
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Add directly into the pool or
spa when no swimmers are present and time is sufficient to
permit even distribution of the chemicals
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Add indirectly in small
amounts slowly through skimmer or overflow to prevent corrosion
of metals
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Add chemicals through feeders
or feeder lines that follow pump and filters, especially DE
filters.
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Add granular chlorine or soda
ash solution directly to the pool, but separately. Always mix
chemicals into plastic containers that have been filled with
water first.
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Add chemicals evenly by
walking the perimeter of the pool.
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Add chemicals to achieve
maximum for Free Available Chlorine, FAC (3.0 ppm) and minimum
pH (7.4) parameters in anticipation of a heavy bather load. This
is an effort prevent falling below minimum standards in FAC
during or following the loading period.
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Add chemicals frequently to
prevent highs and lows in readings. Large reading fluctuations
are hard on soft metals and produces a bounce effect on water
treatment.
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Add additional chemicals only
following an adequate time period that permits a second or third
chemical reading.
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Add chemicals in sequence to
adjust for (1) FAC, (2) Total Alkalinity, (3) pH, (4) Cyanuric
Acid and (5) Total Hardness.
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An effort should be made to
offer adequate time for chemical distribution and most
importantly, a second reading before leaving the scene. Screen
test for pH, FAC and combined chlorine first, and if pH is
extreme, test for total alkalinity. Test for balance or
saturation, TDS and metals can be decided based on the history
of the pool.
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