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Stains & Scale
Ah, the many hues of swimming pool water. A
bit disconcerting when it happens, but at least there's a visual indication of a problem.
Unless your friends are real practical jokers, we'll find the source of colored water to
be either mineral or algae contamination.
Organic problems such as algae and bacteria
can discolor the water and deposit themselves on pool surfaces in a rainbow of greens,
blacks, yellows, pinks. Algae deposits are distinguished from stains in that they are on
the surface and not impregnated into the plaster. A more detailed discussion of their
genesis and eventual destruction is covered in the
algae page.
Other organic materials such as leaves, worms, or other vegetable matter can also
stain pool plaster. An organic stain can usually be removed by sprinkling
granular
chlorine over it. If it doesn't, its probably some other type of stain.
Inorganic materials like
copper,
iron,
magnesium,
calcium or
aluminum can also cloud or discolor the pool water and stain or
scale the pool surfaces, especially the
plaster and
tile grout. When a precipitated
metallic salt such as calcium or magnesium remains in suspension, it can cause turbidity
or cloudiness of the water. When heavy metal minerals are in suspension, they'll color the
water. When these minerals quit floating around and decide to attach themselves or deposit
on interior pool surfaces, the mineral salts such as carbonates of magnesium and calcium
form a whitish crystallized deposit known as scale. If the precipitated minerals have
color, as heavy metals often do, they will deposit themselves in the form of a stain.
So, in summary, precipitated (which means to
come out of solution) carbonates of metallic salts will cloud the water and/or form
crystal deposits on surfaces, while heavy metals will discolor the water and/or deposit
themselves as stains.
Metal
|
Sources
|
Colors
|
|
Calcium |
Plaster, grout, mortar, cal-hypo chlorine shock |
white crystals or precipitate |
|
Cobalt |
Fiberglass Shells |
red, blue, gray, or black |
|
Copper |
Copper algaecides, ionizers, corrosion of copper
and brass pipes, fittings and heaters |
blue, green and blue/green, black, dark red, or
teal |
|
Iron |
Well water, corrosion of iron pipe and fittings |
dark, red, brown, black, gray or green |
|
Manganese |
Well water |
pink, red, black or red |
Minerals like iron,
calcium and copper exist naturally in trace
amounts in your pool water. They may originate
from the source water, that is, the water used
to fill the pool. Well water is notoriously high
in mineral content. Not much we can do about
minerals entering in this manner. Other means of
entry are more controllable.
Iron and copper pipes, fittings and
equipment found in older pools are subject to corrosion by harsh chemical conditions, such
as high chlorine and low
pH. They also erode slowly with the everyday force of water
rushing through. This corrosion and erosion releases heavy metal ions into the pool, which
may be forced out of solution (precipitated), creating dramatic color schemes when free
floating and stains when they deposit themselves.
Another source of metal ions occurs when two
dissimilar metals are placed in close proximity to each other. For example, iron pipe
connected to copper pipe, or a brass valve connected to aluminum equipment. These metals
will attempt to exchange ions; water rushing in between them prevents the exchange,
carrying off bits of their essence to the pool. This is the principle behind
ionization systems.
A frequent source of copper discoloration
and staining is the heat exchanger in the heater. Water rushing through the 8 or 10 tube,
copper finned heat exchanger, at possibly higher than normal flow because of an oversized
pump or faulty bypass valve, or containing corrosive water with high chlorine levels
and/or low pH, will strip the copper right out. Corrosion and scaling conditions are
dramatically increased by the high temperature found in heaters. As heat exchangers erode,
the pool becomes stained and the exchanger tube walls become thin and begin to leak. ($$$)
Finally, staining can occur with the less
than proper use of ionization systems and metal based
algaecides.
Copper is a known algaestat, while silver ions are a good
bactericide. Copper and silver
ionizers inject these metals into the water for contaminant control, however, if the
water
balance is out of control, or mineral levels are too high, staining can occur. The same is
true for the algaecides, although some are chelated, which means they have agents
contained in them to prevent minerals from coming out of solution.
Preventing Mineral Problems
Balanced pool water
is such that it has neither a tendency towards corrosion or scaling. At the most basic
level, pool water must be balanced to control stains and scale. pH or
alkalinity that is
allowed to drift and/or high calcium hardness levels can promote mineral precipitation.
The use of a
sequestering agent (also called chelators) is recommended for pools which have metal plumbing, fittings, heaters, ionizers
or use metal algaecides or fill their pool with well water. These agents keep minerals
tied up in solution like molecular glue.
Correcting Mineral Problems
For pools that are discolored or cloudy due
to precipitated minerals, the path back to blue may be accomplished by:
-
Shock treatment with sodium or lithium
hypochlorite, accompanied by constant filtration and use of a clarifier.
-
Use of a flocculent to drop suspended
particles to the floor for vacuuming.
-
Partial drainage and dilution of the pool
water, especially in cases where the pool is at or near saturation. When
TDS levels are
too high, the water can accommodate no more dissolved material and must throw off some of
it in the form of precipitation. (This is similar to the Jr. High science experiment where
sugar or salt is continuously added to a glass of water until saturation is reached and it
won't dissolve any more).
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