What is pH?
pH
is a scale
measuring
the acidity
or
alkalinity
of a
solution.
The
scientific
definition
is
'the
negative
logarithm of
the Hydrogen
ion
concentration'.
The
pH
scale
is a
measurement
of the
concentration
of acid or
base a
substance
contains and
is
calculated
by
determining
the
concentration
of hydrogen
ions (H+).
High
hydrogen ion
amounts
indicate
high acid
concentration,
low hydrogen
ion amounts
indicates a
basic or
alkaline
concentration.
The pH scale
runs from 0
to 14 with 0
being the
most acidic,
7 neutral,
and 14 being
the most
alkaline or
basic. It is
a
logarithmic
scale, based
on powers of
10, so that
1 pH unit
change
equals a 10
fold change
in H+
ion
concentration!
A pH of 6 is
ten
times more
acidic
than a pH of
7.
The
sanitizing
ability of
chlorine is
achieved by
it turning
into
hypoclorous
acid. pH
affects the
efficiency
of chlorine
by
determining
the amount
of
hypoclorous
acid (free
available
chlorine)
that is
formed.
-
At pH 6.5,
90% of the
chlorine
will be
hypochlorous
acid
-
At pH 7.5,
50% of the
chlorine
will be
hypochlorous
acid
-
At pH 8.0,
20% of the
chlorine
will be
hypochlorous
acid
Unfortunately
you cannot
run your
water at pH
6.5 as it
would be
very acidic
and corrode
any metals
in your
system. The
number one
cause of
heater
failure is
corrosion
due to low
pH. As any
metals
corrode
away, the
resulting
metal oxides
can cause
surface
staining,
and under
some
conditions
even tint
your hair.
Lower pH is
also far
from the
human body's
pH of 7.4
and can be
uncomfortable
to soak in.
At a high
pH, the
water can
make your
eyes sting
and possibly
give you a
sore throat.
A high pH
can also
cause scale
to form.
This is
because at a
pH of around
8.0, the
calcium in
the water
combines
with
carbonates
in the water
to form
calcium
carbonate.
Calcium
carbonate
can form
scale
deposits on
your spas
surface or
in the
plumbing
system. It
can also
form into
tiny
particles
and float
around in
the water
giving it a
cloudy,
turbid
appearance.
The
compromise
is pH of 7.2
to 7.6,
preferably
the midpoint
of 7.4.
Remember, if
your pH
drifts too
high, it
will require
more
chlorine to
get adequate
disinfection.
pH can be
determined
in several
ways. pH
meters
electronically
measure the
ion
concentration,
giving pH in
a digital
readout. pH
indicators
are
substances
obtained
from plant
material
that change
color
depending on
the degree
of acid or
base of the
substance it
is mixed
with.
A few drops
of indicator
is added to
a solution
of the
substance to
be measured.
The color
the
indicator
changes to
is matched
to a color
chart which
matches the
color of the
indicator to
the
corresponding
pH. Some
indicators
have a wide
range of
color
changes from
acid to
base.
Others are
specific to
a small
range with
in the pH
scale, say
2.5 to 5.0
pH. Red
cabbage
juice is a
common
indicator
you might be
familiar
with. Red
cabbage
juice has a
color range
from bright
pink for a
strong acid
to yellow
for a strong
base. Other
indicators,
such as
litmus,
indicate if
a substance
is acid or
base, not
the degree
of acid or
base.
Indicators
can be
soaked into
papers,
making
indicator
paper for
specific pH
ranges.
Indicator
papers can
be dipped
into
substances,
matching the
color change
of the paper
to a pH
color chart
for the
indicator.
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