Getting rid of algae!
Here is an excerpt by two gentlemen, Paul Sears and Kevin Conlin, who did experiments with algae cause and effect and came up with surprising conclusions found here Control of Algae In Planted Aquaria! Paul Sears was gracious enough to allow us to reprint excerpts as well as point to the original article, and here is an update on Paul's aquarium page. Update on Control of Algae in Planted Aquaria We have included the Conclusion below but encourage you to read the whole article.
Conclusion of experiment
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), 12h/day
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.
We are currently utilizing this methods and seeing some very positive results. Of course water parameters
and other factors come into play when figuring the dosing requirements for each individual aquarium and
so there is a little work involved initially to determine the correct proportions. We will update this page as we
work to determine our methodology and report it in as much detail as possible.
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