Control of Aglae in Planted Aquaria
Paul Sears and I have been experimenting with fertilizers in our tank for
a number of years now. A few months ago we noticed that not only are our
plants now growing like crazy, algae of all sorts has just about given up.
What we think is happening is that plant and algae growth in our tanks
has become phosphate limited; that is, there is a slight excess of all
trace elements, micronutrients, K, N, light, and CO2 relative to the
amount of phosphate available. We believe that the plants in the aquaria
are able to utilize phosphate at significantly lower concentrations than
the algae, and the algae has starved as a result.
Together, Paul and I have written the attached paper describing our
observations and hypothesis. One of the surprising conclusions of the
paper is that, in order to get rid of algae, it is necessary to ADD
nutrients, including nitrate, to the tank. We encourage people to try to
reproduce our results and to report their findings in this forum. However,
we must caution against randomly dumping nutrients into one's aquarium in
hopes of making algae disappear. Unless you can compute the ppm
of each element you're adding to the tank when you're experimenting, we
recommend that you stick to commercial products for the time being. And
the algae isn't going to disappear overnight; expect to wait a month or
two for conclusive results.
Right or wrong, we feel this paper is an important step in the right
direction. The truth is sitting out there somewhere laughing at us.
Every careful observation, every clever experiment lets us sneak up on it
bit by bit. One day we will be able to reach out and wring its little
Kevin Conlin kcconlin at cae_ca "We're Canadians. We HAVE to be polite"
Finger as332 at freenet_carleton.ca for PGP public key.
(A copy of this paper will appear soon at http://www.cam.org/~tomlins/)
Control of Algae in Planted Aquaria
Paul L. Sears, Ottawa, Canada, psears at emr_ca
Kevin C. Conlin, Montreal, Canada, kcconlin at cae_ca
Reproduction of this document by any means for commercial purposes
requires the express written consent of the authors.
Experiments with planted aquaria appear to indicate that growth of
green algae, red algae, and cyanobacteria is suppressed in planted
tanks in which the availability of phosphate is the factor limiting
plant growth. It is believed that when light, CO2, N, K, and all
micronutrients and trace elements are present in slight excess
relative to the amount of phosphate available for plant growth,
certain higher plants are able to out-compete algae and cyanobacteria
for the phosphate in the water column, starving them of this essential
nutrient. Two case studies are presented as evidence for this
There are few things as frustrating to the aquarist interested in
growing aquatic plants as algae. After spending a small fortune on
lights, substrate additives, liquid fertilizers, and CO2 systems in an
attempt to get good plant growth, the aquarist is often rewarded with
a lush carpet of algae. Unsightly and stubbornly resistant to
eradication, the algae destroys the aesthetics of the tank while
limiting plant growth by competing with them for light and nutrients.
In desperation, the aquarist experiments with various forms of algae
control, including algicides, bleach dips, antibiotics (for
cyanobacteria), physical removal, and the introduction of an
assortment of algae-eating fish and invertebrates. Feed levels are
reduced, light duration is decreased, and various combinations and
amounts of fertilizer are tried, until through trial and error an
uneasy truce is reached.
In the search for a solution, the aquarist is faced with an almost
complete absence of information as to which of the many tank
parameters should be altered in which order to eradicate algae already
present while still maintaining favorable conditions for plant growth.
This is hardly surprising given the huge number of variables,
including light strength, duration, and spectrum; CO2, micronutrient,
macronutrient, and trace element concentrations; fish load; plant and
algal species and density; and water chemistry and temperature.
Sometimes the information that does exist appears contradictory; in
, excessive growth of cyanobacteria is attributed to high nitrite
and nitrate levels, yet this pest is often seen in fully cycled
aquariums with no measurable nitrite or nitrate at all.
One option available to aquarists with deep pockets is to follow the
proprietary Dupla system , a system of liquid fertilizer drops,
tablets, tap water conditioner, substrate additive, and undergravel
heating coils. Magnificent planted aquaria are routinely produced
this way, but the components are expensive, the ingredients are not
disclosed on the package (but see ), and little insight is gained
into the relationship between plants and algae (or how the system
should be "tweaked" for best results).
Like many others, the authors attempted to grow aquatic plants using
typical aquarium configurations and various commercial liquid
fertilizers and substrate additives. Frustrated by their inability to
attain results even remotely resembling the photographs in the
literature, they began systematically to add specific nutrients to
their tanks and record their observations. Although eradication of
algae was not the immediate goal of the experiments, it was noted that
once the aquarium water was supplemented on a daily basis with trace
elements, micronutrients, and the macronutrients K and N _but not P_,
not only did the plants begin to grow extremely well, algae of all
types began to die off rapidly.
In this paper, case studies of the authors' aquaria are presented.
The case studies are followed by a discussion of the results in which
a number of hypotheses are considered. These hypotheses are quite
testable, and it is hoped that other hobbyists will be willing to
perform controlled studies on their aquaria to either support or
Case Study #1
Initial conditions as of November 1993: 500L aquarium with undergravel
and canister filters; 240W fluorescent lighting, 12 hours per day; 15W
UV sterilizer; 8cm 2mm gravel with a few laterite balls; no CO2
additions; no fertilizer; about 40 3-12cm fish; water temperature 27C,
pH 7.5, GH 100ppm, NO3- 50ppm, 25% change every week; planted mainly
with Hygrophila polysperma and Vallisneria gigantea, with a few
Echinodorus sp., Cryptocoryne sp., and others.
The aquarium was purchased second-hand as a complete set-up and had
been in operation at least six months prior to being acquired by the
author [Conlin]. About a month after after being moved to the
author's residence, a dense coat of green algae developed on the
gravel-coated glass-fiber backdrop. Plant growth was marginal, even
for the H. polysperma, which had small 3cm leaves and was not
spreading. Hygrophila difformis was introduced and promptly lost its
Change: Twenty Terrapur cones were embedded in the substrate and Sera
liquid fertilizer was added as directed to the tank water during water
changes. Hydrocotyle leucocephala was introduced.
Effect: Growth of H. polysperma, H. difformis, and V. gigantea
improved but long strands of green thread algae started growing on the
backdrop. Various Echinodorus and Cryptocorynes showed marginal
growth. The H. leucocephala quickly degenerated, leaving a few small
fragments growing at the surface. Some red algae was noted on the
leaves of Anubias barteri var. nana and along the leaf margins of the
V. gigantea. After a few months, blue-green algae (cyanobacteria)
began to cover the gravel and some plants.
Change: Erythromycin sulfate was added to the water at approximately
Effect: Cyanobacteria disappeared for several weeks but eventually
Change: Less food (particularly frozen bloodworms) was offered to the
fish and a DIY yeast CO2 system was connected to the tank.
Effect: Cyanobacteria remained. Nitrates were unmeasurable. Plant
growth was noticeably faster. Depending on the state of the yeast
reactor, tank pH varied from 6.8 to 7.5.
Change: The Sera fertilizer was eventually discontinued on the
assumption that it was contributing to the growth of the
cyanobacteria. It was replaced with a commercial iron-containing
trace element mix (initially 1/8 tsp of powder a day, soon increased
to 1/4 tsp a day).
Effect: Nitrates rose to about 20ppm. Green algae began to replace
the blue-green algae on the plants and gravel. An iron test kit
indicated the presence of iron at a concentration below the first
level on the color chart (0.25ppm). Plant growth accelerated, but the
leaves on the H. polysperma became bent and the lower leaves fell off.
This was assumed to indicate a potassium deficiency .
Change: K2SO4 was added to the tank at the rate of about 1/4 tsp/day.
Effect: Shortly thereafter the nitrate level became unmeasurable,
leading the author to conclude that nitrogen was now the factor
limiting plant growth.
Change: KNO3 joined the list of fertilizers being added to the tank on
a daily basis. To simplify dosing, the trace elements, K2SO4, and
KNO3 were incorporated into a liquid fertilizer. The mixture was
adjusted to keep the nitrates at about 10ppm when the enough liquid
was added to the tank (about 12mL) to keep the iron at an estimated
Effect: At this point, growth of the H. polysperma, H. difformis, and
V. gigantea became exceptional, requiring weekly trimming. Somewhere
along the line, duckweed had been introduced to the tank and it now
began to clog the surface. Cryptocorynes and Echinodorus began
growing new leaves every few days and sending out runners. Algae of
all sorts quickly declined to the point where careful observation was
required to find it. Strangely, the Echinodorus were unusually pale in
color despite iron fertilization. Magnesium deficiency was suspected.
Change: Epsom salts were added to the fertilizer mix.
Effect: Within a few days, new Echinodorus leaves showed normal
Change: The yeast CO2 system was upgraded to a constant-flow
tank/regulator/needle valve system.
Effect: Reduced pH swings (6.8-7.0). More free time for the author.
Change: After several months, during which plant growth remained
excellent and algae scarce, four pellets of "Vigoro Super Triple
Phosphate 0-48-0" (almost certainly Ca(H2PO4)2) were added to the tank
as an experiment (approximately 0.1ppm phosphate).
Effect: The next day green spot algae was observed on the glass and
Echinordorus leaves, followed two days later by blue-green algae that
grew on some plants and driftwood. Duckweed soon required daily
removal. Nitrates were unmeasurable several days after the phosphate
was introduced but returned to 10ppm a week or so later (sadly, they
weren't measured just before adding the phosphate). Two weeks after
the experiment began, the blue-green and green-spot algae began to
decline, and duckweed growth returned to normal.
Current status: Plant growth remains excellent. Some traces of algae
still remain, principly green spot algae.
Case Study #2
Initial conditions as of May, 1994: 160 L tank, 12 cm of 3 mm gravel
with 1.7 kg of Terralit in the bottom 3 cm. Canister filter with
carbon, 80W of cool white fluorescent light, CO2 fertilization, very
small fish load (6 flame tetras). Water hardness approximately 120
ppm CaCO3 equivalent, pH ~7.0, temperature 25C, 25% change every few
Plant growth was slow, and brown algae that appeared to be a form of
cyanobacteria (rapid growth in sheets, easy to remove) grew on the
plants and substrate. Attempts to control the algae by frequent water
changes and mechanical removal were ineffective. All water changes
were accompanied by disturbance of the top 1 cm of the substrate.
Change: A potassium/iron fertilizer was added (0.9 ppm K, and 0.06 ppm
FeIII) to the replacement water at water changes. The fish load was
increased to 23 flame tetras (6 adult, 17 juvenile) and six
otocinclus. The cool white lights were replaced with inexpensive
Effect: No change noted.
Change: K/Fe addition was stopped, and plant tablets (10-14-8) were
inserted into the substrate in small pieces near plant roots. A total
of 35g of tablets was added over a period of few weeks.
Effect: Some improvement in plant growth was observed. Unicellular
green algae proliferated, reducing the visibility in the water to as
low as 25cm. Frequent water changes had little effect on the algae.
Change: Fritz Super Clarifier (active ingredient(s) unknown) was added
as directed to the tank water.
Effect: The unicellular algae became trapped by the filter. Because a
recurrence was expected if the aquarium parameters were not altered,
another change was made immediately:
Change: Addition of trace elements (homebrew formulation of Fe, Mn,
Cu, Zn, B, Mo, and EDTA) with potassium sulphate at water changes.
The dosage was computed to give 0.1ppm iron and about 1ppm potassium
in the replacement water. Carbon was removed from the filter.
Effect: Plant growth improved, but blue-green cyanobacteria appeared
and began to spread. Nitrates were found to be unmeasurable.
Change: Addition of potassium nitrate began in 1-2ppm NO3- doses,
initially once every 5 days, increasing to daily once the author
[Sears] became convinced of its lack of toxicity at these
concentrations. Potassium sulphate, previously added to replacement
water, was now dosed with the potassium nitrate at about 1-2ppm K. A
commercial trace element mix (composition given in Appendix A)
replaced the homebrew formulation. Magnesium sulphate addition was
begun shortly after at a concentration of about 0.25ppm Mg.
Effect: Significantly better plant growth, but patches of
cyanobacteria continued to grow on the plants and substrate. Green
thread algae appeared on the brightly lit parts of plants. It was
found that nitrate introduced to the water in 1-2 ppm doses was not
detectable one or two days later.
Change: More plants were added. In the process, several old plants
were uprooted, exposing the buried fertilizer tablets to the water.
Effect: Increase in green algae and blue-green cyanobacteria.
Change: Disturbance of the gravel at water changes stopped.
Specifically, gravel vacuuming was discontinued, and replacement water
was poured into the tank gently. Since the substrate evidently still
contained considerable phosphate in the form of undissolved fertilizer
tablets, it was thought best to disturb it as little as possible.
Effect: Algae of all types declined rapidly. It no longer appeared on
the leaves of fast-growing plants, and apparently died and fell off
the older leaves of slower-growing plants.
Change: Reduction of hardness of water to 60 ppm CaCO3 equivalent.
This resulted in a drop of pH to approximately 6.7 (which was the
reason for the change), and a temporary jump in the iron concentration
in the tank, from less than 0.2 ppm to 2 ppm.
Effect: All Cryptocoryne sp. in the aquarium lost some leaves. Algae
continued to decline.
Current status: All of the plants in the tank are growing well,
including the Cryptocorynes that lost their leaves. Stem plants
require weekly trimming, and floating plants need thinning every few
days. The only algae in evidence are some small patches of
cyanobacteria on the substrate and a little green algae on brightly
lit parts of the Vallisneria gigantea, the Cryptocoryne Balansae and
the Bacopa Caroliniana. Disturbance of the substrate (for replanting
of cuttings) has led to minor algae outbreaks (green algae if the
nitrate concentration is at least few ppm, cyanobacteria otherwise).
Small amounts of (apparently dying) material are still in evidence on
some of the oldest Anubius barteri var. nana leaves. The water change
frequency has been reduced to 25% every two weeks.
The observations in the case studies are consistent with the following
hypothesis: when light, CO2, N, K, and all micronutrients and trace
elements are present in slight excess relative to the amount of
phosphate available for plant growth, certain higher plants in the
aquaria are able to out-compete algae and cyanobacteria for the
phosphate in the water column, starving them of this essential
Exactly why higher plants should be able to outcompete algae for
phosphate is unclear. Perhaps their roots give them some advantage,
or they simply need much less phosphate than algae to thrive. Nor is
it known which of the many plants in the test aquaria are responsible
for stripping the water of phosphate, although the fast-growing
duckweed and stem plants with roots growing above the substrate
(notably Hygrophila spp.) are likely culprits. That phosphate is the
factor limiting the plant and algae growth in the test aquaria has
been reasonably well established; it is the only known plant nutrient
not added to the 500L tank in any form other than fish food, and
deliberately adding concentrated phosphate to this tank induced almost
immediate algae growth (and a rapid duckweed explosion too). Since
the plants continue to grow very well, they are clearly gaining
preferential access to whatever phosphate is available. There may be
some literature unknown to the authors that offers an explanation. If
not, it should be fairly easy to conduct controlled experiments with a
sensitive phosphate test kit and a few spare tanks containing only
algae, one or two plant species, and nutrients. An experiment that
shows that duckweed thrives at phosphate concentrations as low as X
ppb, but green algae and cyanobacteria require significantly more than
X, would offer strong support for the hypothesis.
According to the hypothesis, If the higher plants are unable to
utilize all of the phosphate present in the water column because of a
deficiency of some other nutrient, algae will thrive. The type of
algae appears to depend on the availability of other nutrients. In
the test aquaria, it was found that when nitrates were unmeasurable,
cyanobacteria predominated. It is suspected that nitrogen deficiency
favors the growth of cyanobacteria because these organisms can fix the
atmospheric nitrogen dissolved in the aquarium water. When nitrates
were available, green algae predominated. Some red algae was also
observed in the 500L tank before CO2 fertilization was introduced.
Because others have observed that tanks with CO2 fertilization have
relatively little red algae , it tempting to speculate that at
least some red algaes are able to utilize bicarbonate, giving them an
advantage in aquaria where most of the available carbon is in this
form (typically those with high carbonate hardness and high pH). The
following paragraph summarizes the apparent relationship between
nutrients, plants, and algaes:
If the aquarium is P limited, higher plants will outcompete algaes
of all types for P, and the algae will disappear. If not, and N in the
form of nitrates and ammonia is deficient, cyanobacteria will thrive,
otherwise green or red algae will predominate. Red algae is favored
over green algae if most of the available carbon is in the form of
The factors that determine which species of algae will predominate in
a given situation have obviously been greatly simplified. In , for
example, nitrate concentrations in excess of 30ppm are claimed to be
detrimental to the growth of green algae but not to cyanobacteria, so
one would predict that cyanobacteria would predominate at high nitrate
There is a tradition in the hobby of using fish food (usually
processed by the fish first) as the source of all macronutrients for
the plants in an aquarium. When this is done, it appears that first K
and then N become the factors limiting plant growth (i.e. there is
insufficient K and N in the food relative to the amount of P, at least
for the fish foods the authors use). Thus, supplementary K and N must be
added or free phosphate will be available to fuel algae growth (this
contradicts the prevailing wisdom in the aquarium hobby that one of
the ways to reduce algae growth is by reducing fertilization; in fact,
additional nutrients are required). Other alternatives are to
restrict feeding to the point where the growth of algae due to unused
P is tolerable (another common piece of advice), an approach likely to
result in poor plant growth due to nutrient starvation, or to use a
Some of the plant species in the 500L tank grow very slowly compared
to the same species in the 160L tank (Echinodorus sp. in particular).
The 160L tank has an enriched substrate with no deliberate water
circulation, whereas the 500L tank has a relatively inert substrate
with a 300gph UGF. It is highly unlikely that all plants are equally
adept at extracting phosphates directly from the water column, and it
appears that the fast-growing plants in the 500L tank are depriving
the other plants of this nutrient which (thanks to the UGF) is
distributed evenly throughout the tank. Slow-release phosphate
tablets will be placed around the roots of these plants to see if
growth improves. Both authors agree that the substrate design of the
160L tank (solid fertilizer at the bottom of an inert substrate) gives
the better results, probably by making phosphate more-or-less equally
available to all plants without allowing too much to leach into the
water column where it is available to algae.
Despite the lack of controls on the various experiments, and the
inability of the authors to directly measure phosphate in the aquaria,
there is compelling evidence to support the hypothesis that all types
of algae (including cyanobacteria) can be effectively controlled in
planted aquaria by ensuring that phosphate is the factor limiting
plant growth. In two aquariums with different volumes, substrates,
lighting, and plant, algae, and fish populations, effective control of
algae was achieved by enriching the tank water with CO2,
micronutrients, trace elements, N, and K. Despite high initial algae
loads, these tanks are now almost free of visible algae and have
remained so for several months. Furthermore, in the 500L tank it was
shown that phosphate limiting was occuring by adding phosphate to the
tank water and observing the almost immediate growth of green spot
algae and cyanobacteria. It has also been shown in the 160L tank that
disturbances to the phosphate-containing substrate result in algal
growth if there is significant (more than approximately 1 ppm) nitrate
in the water, and in growth of cyanobacteria if nitrate is not present
at this level. It is important to note that plant growth in both
tanks is excellent, so algae control has not been achieved at the
expense of the plants.
Plants cannot grow without phosphate. However, in order to keep a
planted aquarium relatively algae free, free phosphate in the water
column must be minimized. The following recommendations will help
achieve this goal:
(a) A slight excess of light, CO2, K, N, micronutrients, and trace
elements should be maintained to allow the plants to utilize all of
the available phosphate. The authors recommend the following:
20-60 lumens/L illumination (about 2-4W fluorescent light per gallon),
Since inexpensive tests are not available for trace elements,
micronutrients, or K, these items are dosed as some percentage of the
measurable nutrients. The authors have had considerable success with
mixtures that duplicate the relative concentrations present in Tropica
Master Grow fertilizer . For those readers wishing to "roll their
own", a balanced fertilizer recipe is given in the Appendix. Various
commercial aquatic plant fertilizers are also available, but it may be
necessary to purchase several products to ensure complete nutrient and
trace element coverage. Daily dosing is highly recommended because it
may prevent temporary nutrient depletion, which could make phosphate
available on an intermittent basis and prevent the algae from
As a general approach to optimizing plant growth and reducing algae,
the following procedure is suggested:
(1) Set the light and CO2 levels.
(2) Add an iron-containing trace element mix (preferably one that
already has Mg) to the tank every day, adjusting the quantity
on a regular basis to achieve the target iron level. For
mixes without Mg, add Epsom salts as well in the ratio of about
1.5-5.0ppm Mg to 1ppm Fe.
(3) A week or so after reaching the target Fe level, check the nitrate
level. If nitrates are below about 2ppm, proceed to the next step.
Otherwise, add enough K2SO4 to the tank every
day to drop the nitrate level to as close to zero as possible
and keep it there (if the nitrates
don't drop, then something other than K is limiting plant growth and
some detective work will be required to find it). Incidentally,
measuring the nitrate level is helpful for general tweaking; if adding
nutrient X causes the nitrate level to drop, then the tank is probably
deficient in X.
(4) Add enough KNO3 to the tank every day to get a 3-5ppm nitrate reading
(one of the authors [Conlin] obtains satisfactory results with 10ppm).
Once the relative amounts of trace elements, K2SO4, and KNO3 have been
determined, it becomes a simple matter (if desired) to concoct a
liquid fertilizer that can be poured into the tank each day. Using a
mix of dry powders is not recommended as powders tend to separate.
The procedure just described ensures that there will always be a
slight excess of nitrogen in the tank. Some terrestrial plants will
not flower if nitrogen is abundant, and this may be the case for some
aquatic plants too. It would be an interesting experiment to withhold
fertilization for several weeks after a lengthy period (say 6 months
to a year) of good plant growth to attempt to induce flowering.
There is a possibility that some of the trace elements will accumulate
over time to levels toxic to plants if regular water changes are not
done. 25% water changes every second week should prevent this from
(b) Grow fast-growing plant species that can efficiently extract
nutrients directly from the water column. These plants will rapidly
strip phosphate from the water, making it unavailable to algae.
Floating plants (Lemna minor, Limnobium laevigatum) and stem plants
that grow roots at internodes (Hygrophila sp.) are suggested for this
(c) Enriched substrates are probably the best means of supplying
phosphates to plants provided steps are taken to minimize the leakage
of phosphate into the water column. Substrate fertilizers such as
Pond Tabs should be buried deep in the substrate where their nutrients
are preferentially available to plant roots. Substrate circulation
should be minimized to prevent phosphate from leaching too rapidly
into the water column. Avoid gravel cleaning and other substrate
disturbances if at all possible. Eliminating substrate circulation
completely would not be desirable (even if it were possible) because
supplementary fertilizers are usually added to the water and must be
transported to the roots somehow.
(d) There will always be some residual algae in a planted tank because
it is impossible to keep the water completely phosphate free. The
amount of residual algae will be very small, but a good selection of
algae-eating fish (otocinclus sp., farlowella sp., ancistrus sp.,
Crossocheilus siamensis) and invertebrates (Caridina japonica shrimp
and some snails) is desirable anyway for controlling the algae
outbreaks that occur when the tank is first set up, the substrate is
disturbed, or the nutrients are incorrectly dosed.
(f) Do not use phosphate buffers to control pH. Use of these buffers
may produce phosphate concentrations as high as 100ppm, almost
certainly resulting in very impressive algae blooms.
(g) Algicides such as simazine and copper are not recommended because
they damage plants and may be unhealthy for fish as well .
(h) Miscellaneous considerations:
Tap water is not recommended as a source of trace elements because it
may be deficient in one or more elements, and rapid plant growth is
likely to deplete the elements far more quickly than they can be
Certain water treatment products (Aquasafe, NovAqua) should be avoided
as they bind metals (including iron), making them unavailable to
plants. They may also contain phosphate buffers. Simple
dechlorinators or products such as Amquel are a better choice for
treating tap water during water changes.
Carbon filtration may remove necessary trace elements from the water.
With regular water changes and good plant growth, carbon filtration is
not necessary and should be omitted.
(i) As a general principle, avoid adding fertilizers, water
treatments, or any other products to one's aquarium unless the
products completely disclose the concentration of each ingredient
present. Otherwise, there is no way to knowing what effect (if any!)
these products will have on the aquarium's inhabitants.
The authors would like to thank Ed Tomlinson for running various
experiments on his tanks on our behalf. Various participants in the
Aquatic Plants internet mailing list (too numerous to list here) have
contributed many useful observations and insights. Finally, the
efforts of the reviewers, Dave Huebert and Karen Randall, are greatly
 Baensch, H. and Riehl, R. "Aquarium Atlas", Tetra Press, 1987.
 Horst, K., and Kipper, H. "The Optimum Aquarium", AD aquadocumenta
Verlag GmbH, 1986.
 Booth, George "[F][plant] CARBON as a SUBSTRATE", rec.aquaria newsgroup,
8 Aug. 1994 (also available on the Web at
 Frank, Neil "Nutrient Deficiency Symptoms",
 Baensch, H. and Riehl, R. "Aquarium Atlas Volume 2", Tetra Press, 1993.
 Christensen, Claus "Re: Tropica Fertilizer", Aquatic Plants Digest V1 #165,
5 July 1995.
 Frank, Neil "Chemicals to Control Algae - The Use of Simazine",
The Aquatic Gardener, Vol. 4 no. 6, 1991 (also available on the Web at
 Gargas, Joe "Chemical Treatment of Ectoparasites Afflicting Fish Part I",
Freshwater and Marine Aquarium, Oct. 1993.
Appendix A - Fertilizer Recipe (Poor Man's Dupla Drops)
1 Tbsp (~9g) Chelated Trace Element Mix
(7% Fe, 1.3% B, 2% Mn, 0.06% Mo, 0.4% Zn, 0.1% Cu, EDTA, DTPA)
2 Tsp (~14g) K2SO4 (potassium sulfate)
1 Tsp (~6g) KNO3 (potassium nitrate)
2.5 Tbsp (~33g) MgSO4.7H2O (fully hydrated magnesium sulfate, aka epsom
salts; omit if already present in trace element mix)
300mL distilled H2O
0.5mL 9M HCl (optional)
(Most of the ingredients can be purchased at hydroponics shops
or garden supply stores. Epsom salts are available inexpensively at
Dissolve the trace element mix in 150mL distilled water, then add the
remaining ingredients. Pour in additional water to make 300mL
solution. The HCl helps prevent the growth of fungus and may be
omitted if the mix is kept in the refrigerator. Add enough mix to the
tank every day to keep the Fe level at about 0.1ppm (the exact amount
will have to be determined by experimentation, but 3mL per 100L tank
water is about right for a tank with rapidly growing plants). Measure
nitrate levels regularly, and adjust the amount of KNO3 in the mix to
maintain 3-5ppm (this step is fairly important). Those concerned
about adding nitrates to their aquarium can dose the KNO3 separately,
omitting it initially and adding it later as required to obtain the
The shelf life of the solution is unknown. Make small batches, or
store only dry powders (but mix them with water before adding them to
If test kits are not available, satisfactory results can be obtained
by adding 1mL mix to 10L replacement water during water changes.