The following descriptions and control techniques are for common
types of algae found in freshwater aquaria.
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- Algae Types:
- Algae-Eating Fish:
Siamese Algae Eaters,
There are two categories of algae of concern to aquarists: "good" and
"bad". Good algae is present in small quantities, is indicative of
good water quality and is easily kept in check by algae eating fish or
simple removal during routine maintenance. This algae is a natural
consequence of having a container of water with nutrients and a light
Bad algae is either an indicator of bad water quality or is a type
of algae that tends to overtake the tank and ruin the aesthetics
the aquarist is trying to achieve. The label of "bad" is entirely
subjective. For example, one type of green, hair-like algae is
considered a plague by some American aquarists, yet is cultivated
by European aquarists as a valuable addition to most tanks, serving
as a dietary supplement for the fish.
Grows rapidly in blue-green, slimy sheets. Spreads rapidly over
almost everything and usually indicates poor water quality. However,
blue-green algae can fix nitrogen and may be seen in aquariums with
extremely low nitrates. Sometimes seen in small quantities between
the substrate and aquarium sides. Will smother and kill plants.
This is actually cyanobacteria. It can be physically removed, but
this is not a viable long term solution as the aquarium conditions are
still favorable for it and it will return quickly. Treatment with 200
mg of erythromycin phosphate per 10 gallons of water will usually
eliminate blue-green algae but some experts feel it may also have
adverse effects on the biological filter bed. If erythromycin is used
for treatment, ammonia and nitrite levels should be carefully
Forms in soft brown clumpy patches. In the freshwater aquarium, these
are usually diatoms. Usually indicates a lack of light or an excess
of silicates. Increased light levels will usually make it disappear.
Easily removed by wiping the glass or siphon vacuuming the affected
Green unicellular algae will sometimes reproduce so rapidly that the
water will turn green. This is commonly called an "algae bloom" and
is usually caused by too much light like direct sunlight.
An algae bloom can be removed by filtering with micron cartridges or
diatom filters. UV sterilizers can prevent the bloom in the first
place. Green water is very useful in the raising of daphnia and brine
Grows on the aquarium glass and forms a thin haze. Easily removed
by wiping the glass. Considered normal with the higher light levels
needed for good plant growth.
Grows in thin, hard, circular, bright green spots, usually on the
aquarium glass but also on plants under high light conditions.
Considered normal for planted tanks. Must be mechanically removed.
On acrylic aquariums, use a cloth pad or a gentle scouring pad like a
cosmetic "Buff-Puff" and a lot of elbow grease. On glass tanks,
scraping with a razor blade is most effective.
Grows mostly on plant leaves as separate, short (2-3mm) strands.
Considered normal. It might be a less "virulent" form of "beard"
algae. Easily controlled with algae eaters such as black mollies,
Otocinclus, Peckoltia and siamese algae eaters.
Grows on plant leaves and is bright green. Individual strands have a
very fine texture but it grows in thick patches and looks just like a
green beard. It grows up to 4 cm. It cannot be removed mechanically.
This does not indicate bad water quality but grows very fast and
overtakes the tank, making it a "bad" alga. Can be eliminated with
Simazine (Aquarium Pharmaceuticals "Algae-Destroyer").
Grows in bright green clumps in the gravel, around the base of plants
like Echinodorus and around mechanical objects. It has a coarser
texture than "beard algae". Beard algae will ripple in the water
current, hair algae tends to form matted clumps. Individual strands
can get to 5 cm or more. This is easy to remove mechanically by
twirling a toothbrush in it. Can be troublesome if left unchecked.
This is a popular food supplement for fish among European aquarists.
Grows in long, thin strands up to 30 cm or more. Tends toward a
dull green color (hard to tell because it is so thin). Usually
indicates an excess of iron (> 0.15 ppm). Easily removed with a
toothbrush like hair algae.
Looks like individual strands of hair algae but tends to grow in
single branching strands like a deer antler and is grey-green. Seems
to grow mostly on tank equipment near the surface. Difficult to
remove mechanically. Soak affected equipment in a 25% solution of
household bleach and water to remove it.
This grows in feathery black tufts 2-3 mm long and tends to collect on
slower growing leaves like Anubias, some Echinodorus and other wide
leaf plants. Also tends to collect on mechanical equipment. This is
actually a red alga in the genus Audouinella (other names:
Acrochaetium, Rhodochorton, Chantransia).
It cannot easily be removed mechanically. Remove and discard the
affected leaves. Equipment can be soaked in a 25% bleach solution,
then scrubbed to remove the dead algae. Siamese Algae Eaters
(Crossocheilus siamensis) are known to eat this algae and can keep
it in check. A more drastic measure is treatment with copper.
Algal spores are everywhere and will always be present in an aquarium
unless drastic measures are taken. For fish only tanks, a properly
set up ultraviolet sterilizer will kill algal spores in the water and
prevent them from gaining a toehold.
For planted tanks, this is not a good solution since the UV light will
also oxidize trace elements needed by the plants and will limit the
plant's growth potential. Unfortunately, conditions that are good for
growing plants are also good for growing algae. Fortunately, plants
will usually out-compete algae for the available nutrients. However,
if there is an imbalance of nutrients, algae will opportunistically
use whatever is not used by the higher order plants. Different algae
will utilize different nutrients, causing sporadic outbreaks of new
algae types in apparently stable tanks when a temporary imbalance
An ounce of prevention is worth a pound of cure. To avoid introducing
a new algae type to a planted tank with new plants, a simple bleach
dip seems to work well. Mix 1 part bleach in 19 parts water and dip
the new plant in it for 2 minutes. Immediately rinse the plant in
running water, then immerse it water containing a chlorine remover to
neutralize any remaining bleach. This will kill the algae and only
temporarily slow down a healthy plant. Plants in poor condition may
succumb to this treatment, but they probably would not have lasted
The most effective control of algae in a planted aquaria is via algae
eating fish. It is especially critical in the set up of a new tank to
make sure algae does not get established before the plants have had a
chance to establish themselves. For this reason and to help the
biological filtration get established, it is recommended that some
hardy algae eaters are added right away.
Black sailfin mollies
are excellent candidates for the break-in period
of a planted tank since they are cheap and easy to find. They are
usually considered expendable and are removed after a month or so. It
is important to NOT FEED THEM. If they are fed, they will not be
quite so eager to consume algae. When they are hungry, they are eager
consumers of most algae types seen during the break-in period.
are diligent algae eaters, but are best kept in schools
due to their small size. One per 10 gallons is a useful rule of thumb.
Various species of otos are seen in the shops at various times; most
are good algae eaters but some seem to prefer the slime coat on fish
to algae. Unfortunately, there seems to be no way to distinguish the
"attack otos" from normal otos.
Otos seem to be very delicate fish, but this is probably due to
capture and shipping abuse rather than an inherent weakness. When a
fish shop gets some in, it is wise to wait a while before purchasing
to account for die offs. Most people report getting a dozen and
having them die over a period of a few months until just a couple are
left. Those then seem to last for a long time.
Plecostomus is the generic name for a wide range of sucker-mouth fish.
Only the smaller types are useful in a planted tank, since the larger
varieties tend to eat the plant right along with the algae. Two
common types that are useful are the "bristle-nose plecostomus" and
the "clown plecostomus" or Pekoltia. Both stay under 4" long and
don't seem to cause too much plant damage. Sometimes broad-leafed
plants like Amazon swords will be scraped a little too closely by
the plecos, so they bear watching.
Their diet can be supplemented by blanched zucchini and bottom feeder
tablets. They also appreciate a chunk of driftwood in the aquarium to
satisfy their need for cellulose. See the
GOOD FIRST FISH FAQ for more
information on keeping suckermouth catfish.
Do not confuse this fish with the
Chinese Algae Eater, which is very aggressive and does not eat algae.
The siamese algae eater, Crossocheilus siamensis, is a very good algae
consumer and is known to eat black brush (red) algae. The only problem
is that these fish are hard to find in the United States
(see the RESOURCES section
of the PLANT FAQ for sources and identification paper).
There are several fish in
this family. The most commonly seen is Epalzeorhynchos kallopterus,
commonly known as the Flying Fox. The Flying Fox is the more
attractive of the two. It tends to have a brownish body with a very
distinct, sharp-edged black stripe with a distinct, thin gold or
bronze stripe above it. These tend to be very aggressive when they
are full grown and don't eat red algae (as far as one aquarium
reference is concerned).
The other member is the Siamese Algae Eater. It is the same shape as
the Flying Fox but tends toward a silverish body with a somewhat
ragged black stripe. There may be an indistinct gold or bronze stripe
above the black. These are definitely not aggressive; they are good
companions for discus and small tetras.
When they are young, the differences between E. kallopterus and C.
siamensis may not be very apparent, especially if you haven't seen
both types together. Unfortunately, most wholesalers don't sell fish
to stores by their scientific name and the common names that are used
sometimes get pretty silly (like "siamese flying fox"). If you
really can't tell which one the store has, buy it anyway, but be
prepared to sacrifice it if it turns out to be the wrong kind (unless
your fish aren't bothered by it, of course).
Farlowella are useful algae eaters although they are very sensitive to
water conditions. They type known as the Royal Farlowella will get
too large for a plant tank and may cause damage.