Algae Control in the Aquarium
Not all algae in the aquarium is necessarily 'bad' - a certain amount is inevitable where there
is water, light and nutrients. However, some types of algae are certainly a nuisance, if for no
other reason than looking unsightly.
The control or prevention of different algae types is primarily about nutrient control, and
the amount of light. There are therefore some general guidelines which can be followed to
help minimise algae:
- Avoid direct sunlight falling on the tank, especially for prolonged periods. Unfortunately, despite the pleasant rippling
light effects provided by sunlight, the rich lighting spectrum of the sun is likely to mean a constant battle against algae in
- Do not leave lighting on for more than 10-12 hours a day. Longer periods are likely to favour
algal growth, rather than promote plant growth.
- Minimise nutrient levels with frequent water changes.
In particular, it may help to keep nitrates, phosphates and
silicates low if you have a persistant problem - either by the use of reverse osmosis (RO) or deionised (DI) water, or specific
adsorption resins (e.g. API Phos-Zorb). However, note that although high levels of such nutrients may encourage algae, it is not
generally possible to completely eliminate algae by attempting to reduce them, as algae can survive at levels below those which can be
measured by a hobbyist test kit.
- Consider adding algae eating fish if appropriate to the setup. These include: suckermouth catfish
(e.g. Ancistrus, Peckoltia and Otocinclus species), the Siamese Algae Eater (Crossocheilus
siamensis) and mollies.
- Note that in planted tanks (which is not really the same as tanks with a few plants in!), the most effective way to control
algae growth is to plant heavily and promote vigorous plant growth of several different species, to out-compete the algae for
nutrients. The management of a planted aquarium is beyond the scope of this article, and will be the subject of a future
article, but an important nutrient with regard to plant versus algae growth in a planted tank is Iron, and controlling levels
of this nutrient is likely to be important.
The taxonomy of algae and related organisms is complex, but for the purpose of identification in the
aquarium, they can be conveniently grouped into the following:
- "Brown algae" (Diatoms)
- Green algae
- Red/Brush algae
- "Blue-green algae" (Cyanobacteria)
"Brown algae" (diatoms)
This is often the first algae to appear in a newly set-up tank, where conditions have yet to stabilise.
It will often appear around the 2-12 week period, and may disappear as quickly as it arrived when the
conditions stabilise after a couple of months.
It is essential to minimise nutrient levels to ensure the algae disappears - avoid overfeeding and
carry out the appropriate water changes, gravel and filter cleaning, etc. Limiting the light will not deter
this algae, as it can grow at low lighting levels and will normally out-compete green algae under
If brown algae appears in an established tank, check nitrate and phosphate levels. Increased water changes
or more thorough substrate cleaning may be necessary. Using a phosphate-adsorbing resin will also remove
silicates, which are important to the growth of this algae. However, as noted above, it is essentially
impossible to totally eliminate algae with this strategy alone. Due to its ability to grow at low light levels,
this algae may also appear in dimly lit tanks, where old fluorescent bulbs have lost much of their output.
If a problem does occur, otocinclus catfish are known to clear this algae quickly, although you may need
several for larger tanks, and they can be difficult to acclimatise initially.
There are some very plausible theories as to why this algae often appears in newly set up tanks and then later
disappears. If the silicate (Si) to phosphate (P) ratio is high, then diatoms are likely to have a growth advantage
over true algae types and Cyanobacteria. Some of the silicate may come from the tapwater, but it will also be leached
from the glass of new aquaria, and potentially from silica sand/gravel substrates to some extent. Later, when this leaching
has slowed, and phosphate is accumulating in the maturing tank, the Si:P ratio will change in favour of phosphate, which is
likely to favour the growth of green algae instead.
A certain amount of green algae is likely to occur in any tank with sufficient lighting. It is eaten by most
algae eating fish and is generally fairly easy to remove from the tank glass.
Hard 'green dot' algae
This appears as small round dots on the aquarium glass. It appears to be a normal part of planted tanks
with higher light levels. Algae-eating fish will not remove this algae and manual removal requires hard
scraping. Magnetic algae scrapers are usually inadequate, unless the edge of one half is used inside the
tank - or use a razor blade.
This occurs as long greenish or grey strands. Some algae eating fish may consume it. It can be removed
manually by winding around a toothbrush.
Brush or red algae can be very difficult to remove manually. It seems to be favoured in tanks with a high
pH and carbonate hardness, leading some to speculate that they may be able to utilise bicarbonates as a
carbon source. Limiting phosphate and silicate (either by using RO/DI water or specific adsorption resins)
should deter this algae. Siamese Algae Eaters (Crossocheilus siamensis) are are often said to be the
only common algae eating fish which will tackle this type of algae, although the common plec appears to eat it too.
"Blue-green algae" is not really a true algae at all, but Cyanobacteria - a group of bacteria capable of photosynthesis.
It can appear as a slimy coating in a number of different colours. It can
smother plants and may release toxins harmful to fish. It can fix nitrogen and may therefore occur in
tanks with zero or very low nitrates (but possibly high levels of other nutrients, particularly phosphate and organic wastes).
It can be removed manually quite easily, as it often forms loose sheets, but it's likely to return quickly. Improving
circulation/aeration in the tank sometimes causes it to decline. It can be treated with erythromycin (200mg/10 gallons)
where antibiotics are available - this may however affect the filter bacteria, so it will be necessary to check for
ammonia and nitrite after dosing.
Fish will not eat this type of algae.
Summary of Algae-eating fish and inverts
|Tiny size makes them ideal for small tanks, do not damage plants.
|Can be difficult to acclimatise initially.
(Hypostomus punctatus, Glyptoperichthys multiradiatus, etc)
|A very hardworking algae eater, which will eat green, brown and brush algae
|May grow too large for many tanks. Its large size and occasionally boisterous nature may cause havoc in planted tanks.
|Siamese Algae Eater
|Eats green, brown and brush algae.
|Often confused with the Flying Fox (Epalzeorhyncus kallopterus), which is more omnivorous.
|Chinese Algae Eater/Sucking Loach
|Good algae eater when young
|May be less inclined to eat algae when older. Can also grow quite large and may become aggressive.
|Bristlenose (Ancistrus) catfish
|Excellent algae eaters, hardy and do not grow large (around 4"/10cm max).
|Individual species may be difficult to identify, although the general care is the same.
|Many attractive species available.
|Some are expensive. Not all species eat algae.
|Some species are efficient algae eaters for medium sized tanks.
|Some are expensive. Require good water quality.
|Well suited to planted tanks and small 'nano' tanks.
|Must only be mixed with small, peaceful fishes - otherwise they are likely to be eaten.