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Algae and Algaecides
Algae are microscopic single celled forms of plant life that are introduced
into the pool water in particular by wind and rain from the atmosphere. Algae
contain chlorophyll and are one of the hardiest and most widespread living
organisms on this planet, existing in over 30,000 different varieties.
There are three main categories that we need to concern ourselves with, they
-usually floating algae, but sometimes cling to walls. Pool water becomes turbid
with a green growth that renders the pool uninviting and dangerous to use by
making it difficult to see the bottom of the pool. Before green coloration
appears, sides of the pool have a slippery feel, water becomes hazy, and
exhibits a high chlorine demand. This is also the fastest growing algae and
accounts for most 24 hr algae blooms.
Mustard (Yellow) Algae:
-appears as a yellow powdery deposit on the pool, usually on the shady side.
Once established, it is chlorine resistant and can exist in the presence of 3-5
ppm free chlorine. This is also a common algae to grow in aquarium in areas that
get little light (like the back glass wall)
Black (Blue-Green) Algae:
-evident by the formation of dime to quarter sized black (or dark blue green)
spots, tenaciously adhering to the pools surfaces. Black algae forms a layered
structure where the first layer, which may be killed by chlorine, protect under
layer from further destruction. Black algae, like mustard algae, is also very
chlorine resistant. This is also similar to the black algae that is often found
on bathroom shower tiles and in silicone seams near the bath. This form of algae
is very slow growing but very hardy, also found commonly in aquariums as dark
blotching on the glass sides.
Algae thrive on sunshine, warm water, carbon dioxide, heavy bather load and
insufficient chlorine residuals. In the spring as the weather begins to warm and
the days get longer, algae spores (seeds) begin to germinate. This is the most
common time to see an algae bloom, a rapid growth of algae from all the spores
that have been collecting in the water over the winter when the chlorine was
kept at a lower level as the pool was not in use. However, it is not uncommon
that algae can get a foot hold any time of the year. An algae bloom can turn
clear clean water into a green swamp overnight.
When visible algae are present, water can turn a green/brown color, tightly
adhering, ugly spots form on the walls and bottom of the pool, odors will
develop, pH can climb (as algae consumes carbon dioxide which helps keep pH
down), and the pool walls become slippery and hazardous underfoot. Once algae is
visible a substantial problem exists. It is important to understand that algae
takes in carbon dioxide and gives of oxygen like most other plants. Most
bacteria found in swimming pools take in oxygen and give off carbon dioxide.
This means that each can use the by-products of the other for growth. Obviously,
it is desirable to use a chemical program that assures both bacterial and algae
control, as the breakdown of one system can cause the failure of the other.
Prevention of algae
To prevent algae from growing in the first place requires only a proper chemical
program of regular pool maintenance. This means keeping the proper pH and
recommend free chlorine residual for your pool. The best algaecide (algae
killer) and algistat (algae inhibitor) is a properly maintained sanitizer level
of 1-3 ppm chlorine or 2-5 ppm bromine for a pool and 3-5 ppm chlorine or 3-6
ppm bromine in a spa. However it should be noted that algae is very rare in most
spas and hot tubs as the "insulating hard cover" does not allow enough
light for the algae to get a foot hold. Algaecides are chemicals added to the
pool water to control algae. While algaecides can kill algae at high dosages,
most are utilized as algistats, preventing algae formation when chlorine is
allowed to become depleted. Consider them as insurance policies against sloppy
chlorination or during periods of low chlorination like in the winter when the
pool is not in use.
There are three main groups of algaecides:
Quats:- the larges selling and lowest priced of the
algaecides. These are most often found in active concentrations of 5-10% Such
"quaternary ammonium salts" are surfactants and if added in excess,
will cause foaming on the pool surface. Surfactants lower the surface tension of
the water and "wet" algae cell walls. This "wetting" splits
open the cell wall and kills the algae. Lower concentrations and amounts of
quats are used to do a similar job of prevention than polyquats. This algaecide
is most often used as the preventative while polyquats are most often used to
get rid of existing algae.
Polyquats:-are non foaming algaecides sold in concentrations
of 30 to 60%. While more costly than quats, polyquat algaecides are very
effective not only on green algae but also with the chlorine resistant mustard
and black algae and work well at destroying visible algae, while quats are more
frequently used as the algae preventative. Polyquats are differentiated from
quats in that they have the word "Poly" at the beginning of the labels
chemical names and concentrations.
Copper Salts:-Copper ion (Cu+2) is a very effective
algaecide and is used in ponds and lagoons as well as pools to kill and prevent
algae formations. The down side to copper usage is stain formation. Over time,
soluble copper salts can precipitate from pool water and deposit on pool walls,
creating a "blueing" effect. Then, in the presence of chlorine, these
salts will turn to cupric oxide that causes grey to black staining of the pool
walls. These copper salts are also formed or are similar to salts formed with
ionizers and some alternative sanitizers like PristineBlue® which proves to be
a better algaecide than sanitizer, they are listed as algaecides and
bacteriostats (hinder growth and breeding of bacteria rather than destroying
Colloidal Silver:- Silver is similar to copper in may ways,
colloidal silver attaches itself to the pool walls and floor, giving these
surfaces a residual and continuing algaecidal action. Silver can also cause a
black staining to occur on pool walls if not carefully administered. Silver is
also a very good bacteriostat that may reduce the need for chlorine. Some
ionizers use copper and silver plates to produce both silver and copper ions in
To Treat Algae.
To treat algae once they taken hold of a pool check pH and adjust if necessary.
Check filtration, filter pressure and backwash if necessary.
For green algae you can use one of two methods or implement
both. Superchlorinate the water with up to 30 ppm chlorine. Then if you like, or
if necessary 24-48 hours later when the chlorine drops to normal levels add a
good all purpose algaecide according to package direction. The next day, vacuum
the dead algae to waste and backwash the filter if necessary. Use of a good
"Floc" can help speed up the settling of dead algae. Backwashing the
sand filter twice a day during this period may assist recovery rate
dramatically. In case of heavy algae growth it may be necessary to repeat
treatment. After algae have been vacuumed, check pH, adjust if necessary, and
institute a program of superchlorination and use of a good all purpose
algaecide. Make sure chlorine level is maintained at proper level to help
For Black or mustard algae. Brush the algae spots vigorously
with an algae brush (or stiff brush). Shut off the pump, and use chlorine
tablets to spot treat the algae spots carefully (this is not a safe practice of
vinyl lined pools, but a good ideal on concrete surfaces). Then pour a good all
purpose algaecide close to or on algae spots in concentration. Allow dissolved
algaecide to contact the algae overnight. Restore water circulation, then brush
dead algae and vacuum to waste. In case of heavy algae growth it may be
necessary to repeat treatment. After algae have been vacuumed, check pH, adjust
if necessary, and institute a program of superchlorination and use of a good all
purpose algaecide. Make sure chlorine level is maintained at proper level to
help prevent reoccurrence.