Water Balancing
Water balancing is not such a complicated
exercise. It is simply the
relationship between different chemical
parameters. Your water is
constantly changing, year round.
Everything from weather to oils, to
dirt, and cosmetics affect you water
balance. You will probably not change the water in your pool
for many years. Continuous filtration and disinfection removes contaminants which keep the
water enjoyable but this is does not balance your water. A pool that is "balanced" has
proper levels of pH,
Total Alkalinity, and
Calcium Hardness. It may also be defined as
water that is neither corrosive or
scaling. This concept is derived from the fact that
water will dissolve and hold minerals until it becomes saturated and cannot
hold any more water in solution.
When water is considerably less than saturated it is said
to be in a corrosive or aggressive condition. When water is over saturated and can no
longer hold the minerals in solution it is in a scaling condition. So then,
balanced water is that which is neither over or under-saturated. The cliché that
"water seeks its own level" certainly applies here. Water which is under-saturated will attempt to saturate itself by dissolving everything in contact with it in
order to build up its content. Water which is over-saturated will attempt to throw off
some of its content by precipitating minerals out of solution in the form of scale. How do we know when our water is over or under
saturated? We use a good
test kit (with fresh testing
reagents) to
measure the chemical parameters of pH, alkalinity, and calcium hardness.
pH
pH is a measure of how acidic or
basic the water is. pH is a
logarithmic scale from 0-14, with 7
being neutral. Below 7 and a
substance is defined as being acidic,
while levels above 7 are said to be
basic or alkaline. Everything that
enters your pool has a pH value.
Ever heard of acid rain? This is
rainfall with a very low pH. The
human eye at a pH value of 7.35, is just
slightly basic. This is,
coincidentally, in range with proper pH
levels for your pool. To have pH
in balance we adjust the water with
additions of pH increasers (bases) or pH
de-creasers (acids) to
achieve the range of 7.2 - 7.8. If your testing (recommended daily) of the water shows a
pH value below 7.2 the water is in a corrosive (acidic) condition and
you will need to add a
base to bring the pH into a more basic range to prevent corrosion. Conversely, if the pH
is above 7.8, we are in a scaling (basic) condition and must add an acid to bring down the
pH to prevent the formation of scale.
Total Alkalinity
A close cousin
of pH, the level of alkalinity in the water is a measurement of all
carbonates,
bicarbonates,
hydroxides, and other
alkaline substances found in the pool water. pH is
alkaline dependent; that is, alkalinity is defined as the ability of the water to resist
changes in pH. Also known as the buffering capacity of the water, alkalinity keeps the pH
from "bouncing" all over the place. Low alkalinity is raised by the addition of
a base (similar to pH); sodium bicarbonate is commonly used. High levels of alkalinity are
lowered by the addition of an acid (similar to pH). Experts recommend
"pooling" the acid in a small area of low current for a greater effect on
alkalinity. That is, adding an acid will lower both pH and alkalinity. Walking the acid
around the pool in a highly distributed manner is said to have a greater effect lowering
the pH than the alkalinity. Pooling the acid has the opposite effect. A very important
component of water balance, alkalinity should be maintained in the 80-120ppm range
for "gunite" and concrete pools and 125-170ppm for painted, vinyl,
and fiberglass pools. Levels should be tested weekly.
Calcium Hardness
When we speak of
scale, we are talking about calcium carbonate which has come out of solution and
deposited itself on surfaces. It is a combination of carbonate
ions, a part of
total
alkalinity and calcium, and a part of the
Calcium Hardness level. The test for Calcium
Hardness is a measure of how "hard" or "soft" the water is testing.
"Hard" water can have high levels of
calcium and magnesium. If these levels are too high the water becomes saturated and will
throw off excess particles out of solution which then seeks to deposit themselves on
almost any surface inside the pool. This is calcium carbonate scale; a
"white-ish,"
crystallized rough spot. If the levels are too low, the water is under-saturated.
If under-saturated, the
water will become aggressive as it attempts to obtain the calcium it needs. Such
"soft-water"
will actually corrode surfaces inside the pool which contain calcium and other minerals to
maintain its hardness demand. If your Calcium Hardness levels are too high you can use
TSP to lower the levels or a product called
Hydroquest 100. It can also be accomplished by
dilution (adding water to the pool which has a lower calcium hardness content). Levels
which are too low require the addition of
calcium chloride. Recommended range for calcium
hardness is 200-400ppm. Calcium Hardness levels should be tested weekly.
The Saturation Index
Also
called the Langelier Index, this chemical equation or formula is used to diagnose the
water balance in the pool. The formula is "SI = pH + TF + CF + AF - 12.1." To calculate the
Saturation Index, test the water for pH, temperature, calcium hardness, and total
alkalinity. Refer to a chart for assigned values for your temperature, hardness, and
alkalinity readings then add these to your pH value. Subtract 12.1, which is the constant
value assigned to Total Dissolved Solids and a resultant number will be produced. A
result between -0.3 and +0.5 is said to indicate balanced water. Results outside of these
parameters require adjustment to one or more chemical components to achieve balance. This
formula is not guaranteed; however, some readings for pH, calcium, and alkalinity which,
if taken individually would be considered to be well beyond recommendations, can combine
within the formula to produce "balanced water." The SI can be used to pinpoint potential water balance problems. |
