This month's featured article from
Steve's Pool Service
to polish pool water
| Though it's often hard to
describe, you know when you have pool and spa water that has that
something extra - a polish or "snap" - that sets it apart
from the rest.
| If your water has it, great.
If not, hours can be spent adjusting the chemical balance on a pool,
brushing the walls, scrubbing the tile, vacuuming and backwashing the
filter. But if, after all this work, the pool water isn't sparkling clear,
you may wonder, what causing the water to be cloudy? How can that perfect
"snap" be acheived in your pool?
| Good questions. First, let's
look at the cause of the cloudiness.
| Even when you have a
circulation system that is running at optimum capacity and a filter is
doing its job, we know that at best, a filter can remove particles down to
a few microns.
| A micron, as you may or may
not remember from your high school chemistry class, is a scientific term
for a unit of measurement that equals one millionth of a meter - in other
words, really small. To give you an idea how small, the human eye can
recognize things a small as 35 microns. A single grain of ordinary table
salt measures about 90 microns across.
| So if your filter is working
like it's supposed to and filtering out all of the particles larger than
that which can be seen only with the aid of a microscope, what's the
| Well, these tiny particles -
called colloids - are so small that they often lack any real gravity and
usually become suspended in the water. And when you get enough of them in
the pool, they are a real pain the neck when it comes to maintaining water
| Because they are so small,
they can pass right through any pool filter. Because they are not affected
by gravity, they generally will not settle out - they simply remain
hanging throughout the water. And because they reflect light, they make
the water look murky even though you can't actually see them.
| One more thing about these
tiny colloids. Nearly all of them are negatively charged, which is
important because that means they repel each other. They simply can't
combine or neutralize one another.
| Colloids are not the only
things making the water murky. While your sanitizer kills bacteria, once
you've successfully killed these organisms, you're still left with their
tiny skeletons that float in the water.
| And then there are all the
things that are brought in to water by bathers, or blown in from the
surrounding environment. This stuff includes body oils, deodorant, hair
spray, lotions, makeup, sweat, spit, urine, insects, grass clippings,
pollen, smog, acid rain - you name it.
| Most of it can be filtered
or swept out of the water. But some of it can stay around to help cloud or
discolor the water, making it, let's just say less than desirable.
| OK, we now know that the
cloudiness is being caused by all these tiny particles floating around the
pool that cannot be filtered out. But what can we do about it?
has been trying to clear murky, cloudy water for thousands of years.
In fact, in the early days of recorded history, various materials -
like crushed almonds, beans and nuts - were used."
One suggestion would be to somehow
glue all of the particles together until they formed a larger unit,
capable of being trapped by the filter. And this is actually the
principle behind water clarification.
| While it's an idea that has been
perfected by modern science, it is far from new. Mankind has been
trying to clear murky, cloudy water for thousands of years. In fact,
in the early days of recorded history, various materials - such as
crushed almonds and beans in ancient Egypt and nuts in India - were
used to clarify turbid (cloudy) water.
| These early people would store
their drinking water in metal or clay pitchers, throw in some nuts
or beans and wait for the impurities to glom onto them, then skim
off the added material and drink the water.
| This form of clarification used is
a principle now call agglomeration, because the impurities glommed
together before they settled. Individually, the particles were not
heavy enough to be affected by gravity. But once they were
agglomerated, they became heavy enough to settle.
| This process is also called coagluation,
because the dissolved particles form a clot and fall to the
bottom of the water.
| The ancient Chinese found that
they could clarify water effectively using a natural chemical salt,
which scientists in the 19th century identified as aluminum sulfate,
more commonly known as alum.
| Though it was first used to
clarify municipal drinking water in England as early as 1843, the
first municipalities to use it in the United States were in New
Jersey in 1885. The same technology is still in use today by water
companies throughout the world.
| The swimming pool industry has
used alum as a water clarifier since the 1920s, and while limited,
many service technicians continue to swear by its effectiveness
| The ancient Chinese didn't know
how alum worked; they just knew that it did. Today, we know how.
| When alum is added to water, it
forms a gel-like precipitate - aluminum hydroxide - that bridges or
sticks together, forming small bundles that trap suspended particles
as they fall through the water. These bundles are called flocs,
and this process is today called flocculation.
| What is created is a large amount
of sediment on the bottom of the pool, which is made up of both the
gel-like alum precipitate and all the suspended particles and oils
that were in the water. This is usually vacuumed rather that
filtered out, because it tends to be more than the filter can
is more state-of-the-art today to use polymers to bring that
"snap" back to pool water.
| Scientifically, a polymer is a
huge molecule chain that contains many repeating parts. Wood, hair
and rubber are natural polymers, but scientists have imitated these
natural polymers in synthetic polymers that have many uses in the
| Synthetic polymers were first used
as a water clarifier in 1945, but it wasn't until about 1970 that
they were first introduced in the pool industry.
| The key to understanding why they
work as a water clarifier is that each link in the polymeric chain
takes on an electrical charge. If you remember back to our
discussion about colloids, we said that they carried a negative
charge. In fact, most all dirt particles in water are negatively
| A polymer-based water clarifier
carries positively charged ions that are added to the water. One of
the first rules of chemistry is that opposites attract. So we have
all the negatively charged dirt particles attracting themselves to
the positively charged polymer molecules, which get together to form
coagulated clumps or flocs.
| Whether water is cleared by
flocculating, coagulating or agglomerating, what is accomplished is
the gathering together of suspended particles to produce an object
that the filter is physically capable of capturing in its media. In
many cases, this is the exact technology needed to restore pool and
spa water to a state of crystal clarity - the "snap" that
every pool owner wants.
Excerpted from the September 30,
1998 Service Industry News
Story by Doug Walsh
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