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Please
click the Pool Topics Link, on top of every page, to
access a complete listing of Pool Problem subjects, an
alphabetized Website Table of Contents, Pool Equipment
Information, About Alan Biographic Material and a Pool
Glossary. Use the Spa Topics Link, on top of every page,
to access a complete listing of Spa Problem subjects, an
alphabetized Website Table of Contents, Spa Equipment
Information, About Alan Biographic Material and a Spa
Glossary. Use the other links to access additional
subject information. |
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Control of the Langelier or Saturation Index always
starts with a reliable water analysis. The
#2067 ColorQ PRO-9-Plus performs 9 test factors and
a copy of the Saturation Index Calculator. Click
any image for Product and Ordering Information. |
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How to
calculate the Langelier or Ryznar Stability
Indexes? The Langelier
or Saturation Index and the Ryznar Stability
Index use slightly different approaches to solve
and prevent problems, associated with pool and
spa water corrosion and scaling. In some
instances, source water can be so high in
calcium hardness, that is presents a challenge
to avoid scale formation, on the underwater
surfaces. Theses Indexes are intended to
help deal with these problems. If problems
arise, refer to the
Pool Problems
Page or Spa
Problems Page, as a source of
problem-solving information, broken down into
various categories. Scroll down the page and
click on the linked
keywords or
catch phrases
below, to access additional information, on that topic or product.
Calculating Pool and
Spa Volumes
Unsure About Pool or
Spa Interior Surface Areas?
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LANGELIER or SATURATION INDEX |
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The Langelier or Saturation Index is useful in
determining the corrosive or scale-forming
tendencies of pool or spa water. In order to
calculate this Index, it is necessary to have
the following information: |
- pH
Obtained by testing the pool or spa water
- TF
Temperature Factor - using the chart below,
look up the actual pool or spa water
temperature at the time of sampling, in
order to obtain the appropriate TF value.
- CF
Calcium Hardness Factor - determine the PPM
of calcium hardness (CH) in the water
sample. Using the chart below, use the
appropriate calcium hardness (CH) reading,
in order to obtain the appropriate CF value.
- AF
Total Alkalinity Factor - determine the PPM
of total alkalinity (TA) in the water
sample. Using the chart below, use the
appropriate total alkalinity (TA) reading,
in order to obtain the appropriate AF value.
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The ideal range for the Langelier or Saturation
Index is -0.5 to +0.5. Test values more negative
than -0.5 (i.e., -0.6) are considered corrosive
and steps should be taken to adjust the pH,
total alkalinity or calcium hardness, in order
to avoid the effects of corrosion. Test values
higher than +0.5 (i.e., +0.6) are indicative of
scale-forming tendencies and steps should be
taken to adjust the pH, total alkalinity or
calcium hardness, in order to avoid scale
formation and cloudiness. |
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The following formula is used to calculate the
Langelier/Saturation Index:
Langelier Index = pH + TF + CF + AF -
12.1*
* 12.1 is a constant used in the calculation of
the Langelier/Saturation Index
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LANGELIER INDEX CONVERSION CHART |
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TF |
CF |
AF |
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Temp°F / °C |
TF |
CH PPM |
CF |
TA PPM |
AF |
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32°F / 0°C |
0.0 |
5 |
0.3 |
5 |
0.7 |
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37°F / 3°C |
0.1 |
25 |
1.0 |
25 |
1.4 |
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46°F / 8°C |
0.2 |
50 |
1.3 |
50 |
1.7 |
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53°F / 12°C |
0.3 |
75 |
1.5 |
75 |
1.9 |
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60°F / 16°C |
0.4 |
100 |
1.6 |
100 |
2.0 |
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66°F / 19°C |
0.5 |
150 |
1.8 |
150 |
2.2 |
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76°F / 24°C |
0.6 |
200 |
1.9 |
200 |
2.3 |
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84°F / 29°C |
0.7 |
300 |
2.1 |
300 |
2.5 |
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94°F / 34°C |
0.8 |
400 |
2.2 |
400 |
2.6 |
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105°F / 41°C |
0.9 |
800 |
2.5 |
800 |
2.9 |
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128°F / 53°C |
1.0 |
1000 |
2.6 |
1000 |
3.0 |
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The following
example illustrates how the Langelier/Saturation
Index is calculated:
The actual pH = 7.4
The actual water temperature = 78°F or 25°C :
from the chart use TF = 0.6
The actual calcium hardness (CH) = 198 PPM ;
from the chart use CF = 1.9
The actual total alkalinity (TA) = 97 PPM : from
the chart use AF = 2.0
* 12.1 is a constant used in the
calculation of the Langelier/Saturation Index
Langelier Index = pH + TF + CF + AF -
12.1*
Langelier Index = 7.4 + 0.6 + 1.9 + 2.0 - 12.1*
= - 0.2 (from above data)
Results: -0.2 is in the ideal range of -0.5 to
+0.5
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LANGELIER INDEX CORRECTIONS |
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The Langelier
Index is a tool that is most frequently used by
knowledgeable pool and spa professionals. For
the typical pool or spa owner, that maintains
the water balance, within or close to the
recommended ranges for pH, total alkalinity and
calcium hardness, the Langelier Index should not
be a concern, inasmuch as it will fall within
the ideal range of -0.5 to +0.5. In those
instances where the pool or spa water chemistry
is substantially out or balance or problems are
in evidence, the Langelier Index can give
insight into the proper course of corrective
treatment.
Low Langelier Indexes can be raised, to
within -0.5 to +0.5, by adjusting the pH to 7.2
to 7.6, the total alkalinity to 80 to 120 PPM
and the calcium hardness to 150 to 200 PPM for a
masonry pool or spa or 80 to 200 PPM for a vinyl
or fiberglass unit. A low Langelier Index can
result in corrosion, bather irritation and
discomfort.
High Langelier Indexes can be lowered, to
within -0.5 to +0.5, by adjusting the pH to 7.2
to 7.6, the total alkalinity to 80 to 120 PPM
and the calcium hardness to 150 to 200 PPM.
While it is always possible to lower the pH, it
is not as simple with the total alkalinity or
calcium hardness. Lowering the total alkalinity
usually lowers the pH as well. Lowering the
calcium hardness is not always possible, given
the fact that some pools are filled with hard
water. In those situations, where the calcium
level is high, attention should be paid to
lowering the pH and/or total alkalinity as a
means of improving the Langelier Index. A high
Langelier Index can lead to scale formation,
cloudy water, filtration problems, heater
problems, loss of chlorine efficiency and bather
discomfort.
It is not always possible to get the pH and
total alkalinity in range, due to the nature of
the dissolved minerals. pH is always more
important!
To more correctly determine the total
alkalinity, deduct 30% of the cyanuric acid
reading from the total alkalinity test result.
Pool water chemistry is where the path to proper
water quality, clarity and sanitation starts.
Water testing provides the basis for
determining which chemicals are required to
correct and optimize chemical concentrations.
The proper maintenance of the pool water is an
ongoing responsibility and not something to be
taken for granted. Having the right water
testing equipment will make the task easier,
save money on chemicals and help avoid problems.
Become better informed and take charge of your
own water quality!
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RYZNAR STABILITY INDEX |
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An article appeared in the 8/12/11 issue of Pool
and Spa News about the Ryznar Index. This index is
favored, by some heater and equipment
manufacturers, because it affords greater
protection against corrosion, than does the more
familiar Langelier Index. It favors higher
calcium hardness levels and/or higher pH levels.
While this will lessen the possible the
corrosive effects of softer, lower pH water, it
comes at a price. It boosts the calcium hardness
to a point, where scale begins to form, which
actually helps protect the equipment, from
corrosion. However, as scale forms in the
heater, it reduces the efficiency, by acting as
an insulator. In a filter, it acts to cement the
filter media, reducing the effectiveness of the
filter. In areas of the southwest, the water is
already too hard, right out of the tap and it is
challenging to main a clear pool, without
excessive scaling.
If you wish to help protect your heater and
maintain the warranty, you might do one of the
following.
POOLS WITH LOWER TDS AND NOT USING A SALT
CHLORINE GENERATOR: maintain the pH at
7.6-7.8, TA at 120-150 PPM and the calcium
hardness at 250-400 PPM. This will leave you on
the positive side of the Langelier Index.
POOLS WITH A SALT CHLORINE GENERATOR AND
LOWER TDS: maintain the pH at 7-6.7.8, the
TA at 120-150 (if possible) and the calcium
hardness at 250-400 PPM. If the TA is under 120,
keep the calcium hardness closer to 400 PPM.
This will leave you on the positive side of the
Langelier Index.
POOLS WITH HIGH TDS AND NOT USING A SALT
CHLORINE GENERATOR: this usually means that
the calcium hardness is higher than 400 PPM -
even 800 PPM.. Maintain the pH at 7.2-7,4, TA at
80--120 PPM. This will leave you on the positive
side of the Langelier Index. Never use calcium
hypochlorite.
POOLS WITH A SALT CHLORINE GENERATOR AND HIGH
TDS: this usually means that the calcium
hardness is higher than 400 PPM - even 800 PPM..
Maintain the pH at 7.2-7.8 and the TA at 80--120
PPM (if possible). This will leave you on the
positive. high-end side of the Langelier Index.
Never use calcium hypochlorite.
The information is provided as a guide only and
you should check into any special requirements,
that your equipment manufacturer might have. Use
this link to access a Ryznar Index calculator,
which will help you understand the scaling or corrosive
tendencies of water, based on the this index:
www.lenntech.com/calculators/ryznar/index/ryznar.htm |
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