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Simazine - An Algicide


  1. [F] SIMAZINE - article {long}
    by (Neil Frank) (7 Jan 1995)
  2. [F] SIMAZINE - article {long}
    by (Neil Frank) (8 Jan 1995)
  3. [F] SIMAZINE - article {long}
    by (Liisa Sarakontu) (08 Jan 1995)
  4. [F] SIMAZINE - article {long}
    by (Neil Frank) (9 Jan 1995)

[F] SIMAZINE - article {long}

by (Neil Frank)
Date: 7 Jan 1995
Newsgroup: alt.aquaria,rec.aquaria,sci.aquaria

Because of the recent discussion on the potential adverse effects of
Simazine (active ingredient of ALgae Distroyer, and other aquarium
algicides), I offer this previously published article --

                    Chemicals to Control Algae
                       The Use of Simazine
       (Published in Vol 4 no. 6 (1991) of "The Aquatic Gardener," 
            Journal of the Aquatic Gardeners Association)
                           Neil Frank
   There are many products on the aquarium shop shelves which are sold as
products to control algae.  You will probably find that all of them have the
same active ingredient: simazine.  This is short for 2-chloro-4,6-bis
(ethylamino)-s-triazine.  These products are found in liquid, tablet or wettable
powder form, which the consumer puts into solution within the provided
container.  Regardless of the company name, package size or price, the
products are all the same.  But do they work, do they affect vascular plants
and can they harm the fish?
Some History
   Simazine was introduced as an aquatic herbicide with application to control
algae and submerged aquatic vegetation in lakes and ponds in the late 1950's. 
Studies during the 1960's showed that this chemical was effective in
controlling algae and certain species of aquatic plants with no "apparent"
harm to fish.  The chemical was subsequently federally registered as an
algicide for use in aquariums, swimming pools, as well as farm and recreational
   Simazine was first registered for aquarium usage in the multi-ingredient
tablet, "Algae Destroyer," by Aqua-Biotics in 1967.  This registration was
supported by the results of a few phytotoxicity studies in actual aquariums. 
It was not until CIBA-GEIGY (the producer of the chemical) registered its own
product under the brand name Aquazine in 1975 that simazine appeared as an
active ingredient algicide on its own.  Within a few years, several aquarium
products containing simazine as its single active ingredient were similarly
registered by EPA and started to appear on the retailers' shelves.  Now, it
appears that all of the multiple ingredient products are gone and even "Algae
Destroyer" only contains simazine.
   According to available literature, simazine is effective at controlling
unicellular and attached filamentous algae at a concentration of 0.5-1.0
milligrams per liter (mg/l), or parts per million (ppm).  The recommended
usage of aquarium algicides containing simazine as the single active ingredient
yields a value in the middle of this range.  Based on studies in lakes and
ponds, blue-green algae are the most sensitive to treatment by simazine while
diatoms and flagellates are the least sensitive.  As a group, green algae are
only moderately sensitive to simazine at recommended concentrations.  Thus,
the efficacy of the product depends on the type of algae present.  Published
studies as well as CIBA-GEIGY literature point out that submerged aquatic
plants including Myriophyllum, Ceratophyllum and Cabomba, as well as
duckweed and Wolffia can be controlled with simazine at twice the
aforementioned concentrations.  Vallisneria is also reported to be sensitive to
the chemical.. These plants were field studied and are of interest in pond
management because they are considered to be nuisance weed.  Unfortunately,
the use of these plants is different for the aquarist.  Due to the sensitivity of
these reported species to simazine, aquarium plants can be either killed or
have their growth stunted by use of this algicide.  Although CIBA-GEIGY's
Aquazine contains this information on their label, no aquarium algicide product
provides this warning.  Some products do mention, however, as does CIBA-
GEIGY, that caution is needed with water lilies and hyacinths, of interest to
pond users.  Based upon my experience, plants such as Amazon swords and
Crypts are not affected, so the plants to be concerned about may be limited to
Vallisneria, bunch plants and some floating plants.  Fortunately, the latter
tend to be easier and less costly to replace than mature sword or established
How simazine works
   The difference in control among algal species and between algae and higher
plants may be due to differences in cell structure and ease with which
simazine reaches the sites of action.  In order to do its job, simazine is first
absorbed by the algae or plants.  Once inside, simazine moves to the site of
photosynthesis and interrupts food production.  The plant then depletes its
starch reserve and subsequently dies.  Several days are required for
absorption.  CIBA-GEIGY indicates that algae control should occur within 3-14
days after application, depending on the type of algae.  Aquarium algicide
label instructions indicate that a second treatment may be needed in six to
several days.  Based on the manufacturer's recommendations and the above
mechanism of action, I would suggest not reapplying the chemical for at least
several weeks.  It is interesting to note that control of certain submerged
"weeds" is supposed to occur in 4-10 weeks!  Therefore, the effects on
aquarium plants may not be noticed immediately.
Toxicity to Fish
   Studies performed on fish suggest that simazine is not "toxic" at
recommended concentrations.  The species used for these evaluations, however,
are ones of interest to fisheries - trout, minnows, catfish and bluegill.  A
study performed in India where some of their local fish were tested is
probably of more interest to aquarists.  They examined Punctius tico (rosy
barb) as well as Tilapia mossambicum and Heteropneustes fossilis.  The study
found increased hyperactivity, measured by opercular beats per minute, and
mortality at concentrations around 1 mg/l; it suggested a safe limit of 0.1 mg/l
for Punctius tico and Tilapia mossambicum.  In my own experience, I lost adult
Geophagus steindachneri and newly hatched convict cichlid fry in within days
of treating with simazine.  Collectively, this information suggests that simazine
toxicity will be highly variable among fish species and or aquarium conditions.
   Studies in catfish ponds have shown that simazine may slightly depress
fish growth.  Egg hatch and fry growth of fathead minnows also were reduced
with continuous simazine exposure of 1.7 mg/l.  The effect on fish has been
attributed both to direct absorption of the chemical as well as reduction in
dissolved oxygen (DO).  When simazine is used in ponds, DO levels decrease
due to changes in vegetation - decomposition and reduction in photosynthesis
by phytoplankton.  Reduction in DO should not be a problem in aquariums in
which adequate water movement is present with normal filtration and aeration. 
As much algae as possible should also be removed prior to treatment to avoid
problems with decomposition.  These results indicate, however, that long-term
exposure to the chemical should be avoided.
Interactions with the environment
   In laboratory and field tests, higher amounts of silt, clay and organic
matter has been shown to decrease the concentration of simazine in solution. 
In ponds with sandy bottoms, less than one half as much simazine is needed
for equivalent algae control.  Correspondingly, simazine should be more toxic,
both to algae, plants and other aquatic life in aquariums, than with similar
concentrations in ponds because of the difference in available absorbing
materials.  Lower concentrations than those suggested on the product label,
may therefore, be appropriate for aquarium usage.
Concentration build-up
   Simazine has not been shown to accumulate in soil, but concentrations
remain at least 80 percent of applied amounts after 4 weeks.  This is another
concern with repeated doses.  It is also a serous concern with time release
control discs, such as the one Aquatronics came out with in 1985.  The
product, called "Green Water," is intended to "aid in the control and
prevention of green and brown water color, as well as cloudy water." 
Essentially, it is a calcium block with 117 mg of simazine to be used in 25
gallons of aquarium water.  Following package directions, the use of this block
will generate unacceptably high concentrations of simazine.  Assuming that the
disk will dissolve uniformly over the indicated 2 week period, and allowing for
the long persistence of simazine in solution, 1.1 mg/l is expected to remain as
the final concentration after 2 weeks.  The package suggests that a new disk
be added when the od disk has reduced to one fourth original size.  The
directions also indicate that Algae-A-Away should be used prior to starting
the program.  This will add another 0.7 mg/l of simazine.  This, after the first
disk is replace, the simazine concentration will be approximately 1.5 mg/l.  By
the time the second disk dissolves, the concentration should be 2.0-2.5 mg//l
At these levels, may aquatic plants will be affected, as indicated earlier. 
Chronic long-term exposures can also affect the fish.  These simazine
concentrations will be proportionally higher if the product is used in a 20
gallons or smaller aquarium.  Finally, as more disks are introduced, the
simazine concentration will continue to increase, as the simazine saturation
limit in water (5.4 mg/l) is approached.
   Simazine has a place in the management of many species of algae in the
aquarium, particularly the blue-greens.  However, the product must be used
cautiously and sparingly.  Due to the long persistence of simazine, single
doses should generally be considered and large water changes may be
advisable after the algicide has done its job, say in 2-3 weeks. 
Unfortunately, aquarium product label directions are very misleading, if not
incorrect.  Misuse of this algicide may have contributed to many aquarists
becoming ex-aquatic gardeners.
CIBA-GEIGY Corp. "Aquazine, directions for use and conditions of sale and
warranty" (1984).
CIBA-GEIGY Corp. "Aquazine Aquatic Algicide/Herbicide," Technical Bulletin
Mauck, W.L. A Review of the Literature on the Use of Simazine in FIsheries,
U.S. Fish and Wildlife Service (1974)
Tucker, C.S. Consequences of Copper Sulfate and Simazine Treatment for
Phytoplankton Control in Fish Ponds and Studies on the Dissipation of
SImazine in Laboratory Microcosms, Ph.D Dissertation, Auburn University (1978)
Upadhyaya, A. and K.S. Rao, "Acute Toxicity of Tafaxine to Fish," Intern. J. of
Environmental Studies, 15:236-238 (1980)
A version of this article was originally published in Freshwater and Marine 
Aquarium Magazine (FAMA), December 1986, under the title "Algae in the Aquarium, 
Part III - The Use of Chemical Algicides."


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[F] SIMAZINE - article {long}

by (Neil Frank)
Date: 8 Jan 1995
Newsgroup: alt.aquaria,rec.aquaria,sci.aquaria

In article <>,
Jim Hurley <> wrote:
>Good article. Please will someone see that this is archived in the


But, please note the following correction pointed out by
Liisa Sarakontu: 

Puntius tico (Barbus tico) is the Two Spot or Tico Barb, not the Rosy
Barb, as I wrote.  (Barbus conchonius is the Rosy Barb.)  

Thanks Liisa.

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Launchpad is an experimental internet BBS. The views of its users do not 
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[F] SIMAZINE - article {long}

by (Liisa Sarakontu)
Date: 08 Jan 1995
Newsgroup: alt.aquaria,rec.aquaria,sci.aquaria

In article <3eoq7e$> (Neil Frank) writes:

   But, please note the following correction pointed out by
   Liisa Sarakontu: 

   Puntius tico (Barbus tico) is the Two Spot or Tico Barb, not the Rosy
   Barb, as I wrote.  (Barbus conchonius is the Rosy Barb.)  

TICTO, Neil, I said it was TiCto! Barbus ticto, or Ticto Barb. Why don't
you ever listen to what I say?

(Sorry Neil, I know you normally do listen :-)

Liisa Sarakontu

[F] SIMAZINE - article {long}

by (Neil Frank)
Date: 9 Jan 1995
Newsgroup: alt.aquaria,rec.aquaria,sci.aquaria

In article <>,
Liisa Sarakontu <> wrote:
>In article <3eoq7e$> (Neil Frank) writes:
>   But, please note the following correction pointed out by
>   Liisa Sarakontu: 
>   Puntius tico (Barbus tico) is the Two Spot or Tico Barb, not the Rosy
>   Barb, as I wrote.  (Barbus conchonius is the Rosy Barb.)  
>TICTO, Neil, I said it was TiCto! Barbus ticto, or Ticto Barb.

Liisa, you must excuse me -- It is my new computer eye glasses <g>. I was
so distracted that I gave the wrong common name, Rosy barb (mistake #1), that 
I did not notice the spelling error on the species name (mistake #2).
I am almost as old as George Booth, you know <grin>.

Anyway for the FAQ version:  The native fish used in India's Simazine study is
Barbus Ticto (Two Spot Barb).

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