are found throughout nature, and are refined for a variety of
diverse applications. They have a very low acute mammalian toxicity
and a strong buffering capacity, and are known to be
cost-effective, especially for use in swimming pools.
What do borates do?
Arguably the most important function of borates in pool water is to
serve as a buffer, and many of the other attributes stem from this
one. Borates are excellent at holding pH; this is the reason why it
is so difficult to adjust the pH to neutral with some borate
Borates in solution form an equilibrium between the acid
(undissociated) and the borate ion (dissociated and negatively
charged). Between the two, some borate chains are thought to also
occur. It is the interaction of this balance (equilibrium), and its
ability to adsorb acid (protons) and base (hydroxyl groups) without
significantly changing pH, that allow borates to perform so well as
Borates perform as a weak Lewis acid. Most acids donate a proton,
but Lewis acids accept a hydroxyl group (OH-), usually from
B(OH)3 + H2O
B(OH)4- + H+
In a situation with borate in a pool at neutral pH, most of the
borate is present in its undissociated trivalent form, and some is
present as the tetrahydroxy borate anion. When you add acid (H+ or
protons), some of the tetrahydroxy borate anions lose a hydroxyl
group (OH-) to form water with the protons. When you add base
(hydroxyl group or OH-), some of the undissociated tri-coordinated
borate becomes dissociated and tetra-coordinated, absorbing the
base. Thus, the perfect balance is maintained.
Some technicians swear by borates and will use them as a complete
replacement for alkalinity; after all, with the carbonate system it
is continuously being lost from the water as CO2. However, borates
also work well with carbonate and cyanurate to form three layers of
The fact that borates work well with carbonate disproves the common
misconception that they control algae by removing CO2. You are
adding soda ash or bicarb to a pool on a regular basis to maintain
alkalinity, and relying on the carbonic acid carbonate equilibrium
for buffering and to control pool pH. Obviously, the borates did
not “remove” any carbon dioxide; and if even if they
did, the next time you added carbonate, you would be adding more
CO2. Also, there is always enough CO2 dissolving into the water
from the atmosphere to support algal growth.
So how do borates control algae, then? In the simplest explanation,
borates stop the algal cell from both producing food
(photosynthesis) and then eating it (metabolism). They do this by
locking up special molecules in the cell called nucleotide
co-enzymes; these include both NAD+ (nicotinamide adenine
dinucleotide) and NADP+ (nicotinamide adenine dinucleotide
phosphate). The NAD+ is needed and used in metabolism, and the
NADP+ is needed and used in photosynthesis. But they are almost
identical in chemical structure.
Similarly to the way borates can accept a hydroxyl group from water
by behaving as a Lewis acid, they can also accept hydroxyl groups
from organic molecules to form a complex (a bit like a chelate).
This occurs preferentially with sugar alcohols with adjacent
–OH groups due to the enhanced stability of such
The molecules NAD+ and NADP+ have the cis-adjacent hydroxyl groups
(side-by-side OH groups) required for complex formation on a ribose
sugar within the molecule. But in addition to this, the positive
(cationic) charge of the nitrogen (N) within the nicotinamide
moiety of the nucleotide allows for electrostatic stabilization of
the complex with the borate negative (anionic) charge. Providing
the most stable complex in biological systems basically means that
this is where the borate will be most of the time.
It has been concluded that the same mechanism is likely occurring
in all organisms, including algae; however, with algae these
nucleotide co-enzymes are equally important in photosynthesis as
supporting metabolism in the mitochondrion. So in essence, algae
get hit twice.
Borates have been used for many years as corrosion inhibitors,
primarily on steel and zinc. Borates act as non-oxidizing anodic
inhibitors, having insufficient oxidizing power of their own to
affect passivation; but in the presence of oxygen, iron-containing
metals show passivation.
The presence of cloudiness and scale in pools is a major aesthetic
issue. Cloudiness can be caused by a number of factors, only one of
which is water hardness caused by high calcium content, which can
also lead to scale formation. Scale is formed when the
precipitation of salts, such as calcium carbonate or calcium
sulfate, crystallize from solution as scale on the pool sides,
typically at the water surface where evaporation is taking place
and the solution is locally super-saturated. Both problems are also
exacerbated by high pH.
Borates help this problem in two ways. First, they are good
buffers, so they generally reduce the tendency for pH to creep
upwards. Second, they have mild sequestration ability due to their
divalent cation binding property, so they lock up calcium almost
like a chelate. A 1:1 complex of borate and calcium or magnesium
ions is believed to form:
This effect may also contribute to the water clarity observed in a
borate pool, as well as the softer feeling water, which is gentler
on the skin — and which is why borates are also added to
washing detergents and bath salts.
With the recognition of all the benefits borates provide for pool
water, and the technological advances that have overcome the
previously perceived disadvantages of borates (such as low
solubility and high pH), these products are becoming ever more
popular as part of a pool treatment arsenal. With the growing
emphasis on the use of natural products, the protection of
resources and the importance of environmental impact, many
customers are coming to prefer these products as well.