BIO202: Water Balance

1. BIO202: WATER BALANCE
Pool & Spa University

2. WATER BALANCE
➤ There are five main
components to proper water
balance:
➤ TDS
➤ Saturation Index (SI)
➤ pH
➤ Total Alkalinity (TA)
➤ Calcium Hardness (CH)
➤ This course will cover TDS,
Saturation Index, pH, and
total alkalinity.
CH
TA
pH
TDS
SI

3. SATURATION INDEX
➤ Saturation index, also known as the Langelier Saturation Index
(LSI), is an aggregate measurement that is used to determine
whether water is corrosive or scale-forming.
➤ LSI is composed of five measurements: pH, total alkalinity,
calcium hardness, TDS, and water temperature.
0 +0.3-0.3
IDEAL
CORROSIVE SCALE-FORMING
➤ Ideally, the SI would fall between -0.3 and +0.3. It is not possible to
directly “balance” SI; however, making adjustments to its individual
parameters can be done.

4. TDS
➤ TDS stands for “total dissolved solids” and is a measure of any and all mineral material dissolved
into water.
➤ Water is the “universal solvent,” meaning that most everything will dissolve, eventually, in
water.
➤ Everything—chemicals, bathers, debris from the environment—contributes to TDS. Over the
course of a season or several months/years, TDS will rise.
➤ As TDS increases, water takes more time to dissolve chemicals and reduces their efficacy. In
most systems, we consider a TDS reading of >2500ppm (>1500ppm in spas) to be “too
high.”
➤ Saltwater systems will always have higher-than-average TDS due to the dissolved salt in
the water.
➤ Fresh water is necessary in most cases to reduce TDS. For many owners, this will happen
naturally as evaporation, splash-out, and wastewater lost from vacuuming/filter cleaning
occur. Indoor pools and low-use pools will need to supplement with partial drains and refills
on occasion.
➤ It is possible to reduce TDS through reverse osmosis, though this is not available
everywhere and is not as common as partial drains & refills.

5. PH
➤ If you remember from a previous course, pH is a measure of
how acidic or basic the water is, with 0 being acidic, 14 being
basic, and 7 being neutral. But what exactly does pH
measure?
7 140
Corrosive Scale-forming
7.4 7.6
Reminder: for pools and spas, 7.4-7.6 is the ideal range!

6. PH
➤ pH and adjustments made to it are based on the concentration of hydrogen (H+) ions
and hydroxide (OH-) ions. At a pH of 7, the ratio of H+ ions to OH- ions is roughly 1:1.
➤ As the balance shifts toward more H+ ions, the water’s pH decreases; as it shifts
toward more OH- ions, the water’s pH increases.
➤ Anything that can either donate or accept H+ ions can affect pH. In practice, this means
virtually anything added to pool/spa water.
➤ Products that can accept H+ ions will increase pH; products that can donate H+ ions
will decrease pH.
7 140
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
OH-
OH-
OH-
OH-H+
OH-
OH-
OH-
OH-
OH-
OH-
OH-
OH-
H+

7. PROPERTIES OF ACIDIC WATER
➤ Unnaturally clear water
➤ Corrosion of pool surfaces and
equipment
➤ Metal corrosion is particularly
likely and can result in metals
being deposited into the water,
causing surface staining and
water discoloration
➤ Etching of plaster
➤ Wrinkling of vinyl liners
➤ This is often irreversible, as
wrinkles will return even if
machined out
➤ Skin/eye irritation (itchy or burning)

8. PROPERTIES OF BASIC WATER
➤ Cloudy water
➤ Can appear milky white in
systems with high calcium
hardness
➤ Scale formation
➤ Adheres to pool surfaces and
can be unsightly or cause
injury if it forms sharp edges
➤ Forms inside of pool
equipment, causing early
equipment failure
➤ Skin/eye irritation (dry)

9. TOTAL ALKALINITY
➤ Total alkalinity is the measure of
the buffering capacity of the water.
➤ Buffers are weak acids and bases
that are designed to resist rapid
changes to pH; they contribute
H+ ions (or absorb OH- ions)
when a base is added and
absorb H+ ions when an acid is
added.
➤ Major contributors to total
alkalinity can stand on their own to
protect pH, while minor
contributors cannot. (They will still
contribute to the overall total
alkalinity reading.)
Major Contributors
Carbonate
Bicarbonate
Hydroxide
Minor Contributors
Cyanuric acid
Borates
Silicates
Phosphates

10. TOTAL ALKALINITY
➤ When alkalinity is low, the pH will shift rapidly, making
corrosion and scale formation more likely.
➤ It is possible to have a negative alkalinity reading; at pH
readings of <5, the buffering ability of the water will be
completely neutralized. Pools with alkalinity readings less
than zero are considered to have an alkalinity demand and
may require more product than usual to correct the issue.
➤ When alkalinity is high, the pH will shift very little and will
tend to drift up, making scale formation more likely.
➤ In both cases, swimmers may complain of discomfort.

11. TOTAL ALKALINITY
➤ As stated previously, cyanuric acid (CYA) contributes to total
alkalinity; however, it is a weak contributor.
➤ When measuring total alkalinity, it is common to adjust the
final reading based on the results of a CYA test. This final
number is known as “adjusted total alkalinity” or carbonate
alkalinity and, for the purposes of pool testing, is a more
accurate number.
➤ CYA contributes to alkalinity at 1/3 its tested value; subtract
this number from the TA to get the adjusted alkalinity.
➤ Example: Total alkalinity tests at 120ppm and CYA tests at
30ppm. 1/3 of 30 is 10; subtract 10 from 120 to get 110, the
adjusted total alkalinity.

12. BBB?
➤ Some websites will suggest customers follow the “BBB” method to balance pools. The three
chemicals referred to in the process:
➤ Bleach (household strength, usually)
➤ Baking soda (food-grade sodium bicarbonate)
➤ Borax (sodium tetraborate decahydrate, a household water softener)
➤ This is an insufficient method for pool balance for a wide variety of reasons:
➤ All three products have pH readings in excess of 9 and will drive the pH up over time.
➤ Household and food-grade products may not be “pure” and will contribute unwanted additives
to pool/spa water which can result in sanitation and clarity issues.
➤ Desired results may not be achieved by using these products and can be more costly in the
long run to get the same effect as pool-grade.
➤ Pool-grade products like Balance Pak® 100, Optimizer® Plus, and Smart Shock® are
manufactured to dissolve better and deliver consistent results per pound. If buying bulk
products, make sure they’re pool-grade or industrial-grade.
➤ A general rule of thumb: if you wouldn’t bake a cake with BP®100, why would you throw baking
soda in your pool?

13. CONGRATULATIONS!
You have completed the activity!