Laboratory research has shown that when phosphate
is removed from the water, algae
growth is impacted. In such
situations, reason dictates, it is much
easier to control with EPA-registered
algicides — chemical compounds
such as chlorine, bromine, quaternary
ammonia compounds, poly quats,
copper and silver. With less algae to
deal with overall, a registered algicide,
along with a good sanitization program,
can be more successful in keeping pool
water clean and clear.
It’s helpful to think of algae
separately from other pool invaders
such as bacteria. In many cases, pool
professionals lump them together and
rely on chlorine to be the sanitizer as
well as the oxidizer and algaecide in the
pool. Because chlorine can be an EPAregistered
algaecide, the mindset is that
additional algaecide is not needed. Let’s
consider something, however. What is
chlorine’s No. 1 job to do in a pool? It’s
not to kill algae. Chlorine’s No. 1 job is
to kill bacteria. To do that, there needs
to always be a 1 to 4 ppm free available
chlorine residual in the water.
If chlorine is asked to do the work
of killing bacteria and preventing algae,
more chlorine will be necessary to
maintain the residual. Chlorine doesn’t
have a priority list to follow. Consider the
number of times a pool is tested on a
weekly basis and the chlorine residual is
0 ppm. When this occurs, the pool does
not have any protection against algae
or bacteria, and algae can grow and
reproduce quickly.
The use of a preventative algaecide
on a weekly basis is one of the best
products you can incorporate into
weekly pool care to make your pool
maintenance programs as effective
and efficient as possible. Adding
a preventative algaecide, such as
a blended formula, copper-based
algaecide, or a quat- or polyquat-based
product, will provide protection against
algae even if the chlorine residual is
lower than acceptable. Keep in mind
that algaecides do not protect against
bacteria; a free chlorine residual is
essential to kill bacteria and allow for
swimming.
ROLE OF PHOSPHATE IN
ALGAE GROWTH
There is nothing that will replace the
need for an EPA-registered algaecide
as part of regular pool maintenance.
However, a look at how algae utilize
nutrients they have access to can give
us some options for making pool care
programs more efficient and less likely
to lead to water quality issues.
Let’s examine the critical nutrients
for algae. Like human beings, algae need a balanced diet of nutrients to be
healthy, strong, and able to reproduce
to create an algae bloom in a pool.
What happens to algae if we limit one
of those food groups? Let’s apply the
scientific principle called Liebig’s Law
of the Minimum. This Law says that
if you limit one factor that’s necessary
for growth, then you’re going to limit
the overall ability of the system to grow.
The system can survive but will not be
as healthy or strong as possible, which
may limit growth and reproduction.
Nitrogen, phosphorus, magnesium, and
other trace minerals are the critical food
groups that algae need to be able to
grow, reproduce and be healthy.
According to Liebig’s Law of the
Minimum, algae can only grow as strong
as your weakest link. What happens if
one or more of the nutrients that algae
need to grow in a pool are limited? Is
algae cell yield or ability to reproduce
diminished? Let’s focus on phosphate,
which is a crucial nutrient for algae,
as well as something we can test for,
remove, and manage in pool care.
Applying Liebig’s Law of the Minimum
can illustrate how limiting phosphate
availability can create a system where the
amount of algae is easily controlled by
using a preventative algaecide.
Experimental Insights: During extensive
algae research at Biolab, Inc, we set
up controlled environments varying
in nutrient composition to highlight
phosphate’s significant role in algae
reproduction, as well to explore the
impact of magnesium, nitrogen,
and other nutrients on the health of
algae. Samples were set up by adding
a common form of green algae to a
growth medium that contained all the
elements that algae need to grow, minus
one critical nutrient, which differed for
each sample. The control sample had all
the critical nutrients necessary for algae
growth and reproduction.
In one environment, all nitrogen was
omitted, in another the phosphorus, and
in the third bottle, all of the magnesium
was omitted. In the last experiment,
excess calcium was added to the growth
medium.
The control sample after 20 days of growth.
The sample with phosphorus missing from the medium.
Here is the picture of the control
sample after 20 days of growth [top photo above]. It had every nutrient it needed
in excess to grow, reproduce, and be
healthy. As you can see in this picture,
it is healthy. When examined under
the microscope, this sample was
full of healthy cells that were actively
reproducing and growing. Algae, with
access to all nutrients it needs, will
be able to grow and reproduce unless
something is done to stop it.
This picture illustrates the sample
with phosphorus missing from the
medium [bottom photo above]. All other nutrients
and parameters were identical to the
control sample. Out of all the nutrients
tested, phosphate is the one that can be
tested, removed and controlled in a pool
environment. This bottle looks much
different from the control. To be clear,
the algae is not dead, it was just not able
to grow as quickly. By itself, removing
phosphate is not an effective method
to kill or prevent algae. Removing
phosphate will help, but other means are
necessary to ensure the objective.
These algae, with limited access
to phosphate, are not reproducing at the same rate as the control sample.
Under a microscope, the healthy algae
cells are less prevalent, and signs of
reproduction are not as evident. It is
not growing as well as the one with all
the nutrients. Which scenario would be
easier to control with regular weekly pool
maintenance? Is it the control sample
with active growth and reproduction,
or the sample with less growth present
to kill? To be clear, if these bottles also
maintained an appropriate sanitizer
residual and utilized a preventative
algaecide, algae growth would not be
observed regardless of the phosphate,
nitrate, or other nutrient levels.
PHOSPHATE REMOVAL
By removing phosphates from the pool
environment, pool care becomes easier.
The pool water is less likely to end up
turning green overnight or to experience
a recurring problem with algae.
Ideally, phosphate levels should
always be less than 125 ppb in
pools. This can be a difficult task, as
phosphates are constantly introduced
to pools from a wide variety of sources,
including the environment, lawn
care chemicals, rainwater and some
products, just to name a few. The
constant re-introduction of phosphate
to pool water means that incorporating
phosphate removal into part of a weekly
pool care program is the best approach
to keeping levels low. Most phosphate
removers perform one of two functions:
High-level phosphate removal or lowlevel
maintenance removal.
High-level phosphate removers,
which utilize the pool filter for removal,
can remove high levels of phosphate in
short periods of time. Expect temporary
clouding of the water and the need to
rinse or backwash the filter as part of this
process. This is unavoidable because
the only way to remove phosphate is
to force a reaction that pushes it out of
solution. At high levels of phosphate, a
large amount of precipitation is expected
which can temporarily cause cloudiness
until it is trapped in the filter. However,
once phosphate levels are below 500
ppb, weekly or routine maintenance
phosphate removal products can
remove low levels of phosphate to
prevent levels from becoming high and
causing problems. Weekly phosphate
removal can be blended into multifunctional
maintenance products that
may contain the benefits of enzymes
and clarifiers along with phosphate
removal.
CONCLUSION
Algae control in swimming pools
demands a multifaceted approach
integrating regulatory compliance,
chemical intervention, and nutrient
management. By understanding the role
of essential nutrients like phosphates in
algae growth and employing targeted
interventions in addition to the weekly
addition of an EPA-registered algaecide
and sanitization program, pool
operators can effectively prevent and
manage algae outbreaks. And that will
help them effectively manage their
pools.
This article first appeared in the September 2024 issue of AQUA Magazine — the top resource for retailers, builders and service pros in the pool and spa industry. Subscriptions to the print magazine are free to all industry professionals. Click here to subscribe.
