Algae In Garden Fish Ponds & How To Control It 100% Effectively In Your Koi Pond
Algae are tiny plants. They like sunlight and grow rapidly when fed nutrients in
the form of nitrogen chemicals (like nitrates that develop naturally in all
garden fish ponds).
Algae therefore need food, oxygen and sunlight to grow and survive.
Like most of us the more food, the more oxygen and the more sunlight the better
and bigger the algae grow. In the right conditions the algae grows at an
explosive rate - 30 times per hour!! This is why a swimming pool can be perfect
one day and the next day it is totally green. You say how to yourself how can
this be this possible? - Now you know why.
Blanketweed and String Algae
Not all algae are green and not all algae are minute in size and nor do they all
remain suspended in water giving that pea-soup appearance. Some algae join
together as a long straight line and create long slimy strands yet the water
remains perfectly clear (blanketweed). Other algae grow to about 1 to 2 cm in
length and stick to pond surfaces, waterfalls or rocks etc.
The trouble caused by algae in ponds can range from one of inconvenience to
Algae can create bright green totally opaque pond water caused by millions of
algae cells congregating towards the surface of the pond. This condition is
often referred to pea-soup water.
Algae grow inside pipes and block the pipes. This has been the cause of ponds
being pumped dry. If the blockage occurs on the outlet from the gravity flow
filter then the pump will continue to pump into the filter and overflow from the
lid. It is therefore a good idea to always position a filter in such a way any
overflow finds it way back into the pond.
Algae blooms in prolonged periods of hot weather can result in significant fish
mortalities as a direct result of extracting all the dissolved oxygen from the
Pond Algae ...
It is not necessary to give the Latin names and species. What is important is
the practical understanding of the situations you will encounter.
By way of general background it is important to realise that algae thrive on
sunlight, warm weather and high nutrient levels in water. So if you have a
problem it will possibly disappear in winter and be extremely concerning and
annoying in mid summer. Algae problems have been getting worse over the years as
a result of more nutrients (fertilisers for the algae, which are plants
remember) finding their way into waterways and natural water supplies.
Because of the need for sunlight algae will tend to congregate at the surface as
much as possible this is one reason why blanketweed forms dense floating mats.
Aquatic Plants and Algae
If a pond has plants then these plants will compete with algae for the available
nutrients. In this way algae problems can be reduced but possibly not
eliminated. For this reason if no other it is a good reason to introduce a range
of aquatic plants into a pond or the circulating water system.
Fish eat plants so many pond keepers plant waterfall areas or even create a
separate pond just to hold plants.
In ponds that contain only plants the problem of algae is normally much reduced
for the reasons that nutrients from fish food are then eliminated.
Even in fishponds it makes sense to always underfeed fish to reduce algae
problems fish can live quite easily on what is naturally available in most
ponds so long as the pond is not over-populated.
First of all the usual problem of green water (sometimes brown) which does not
go clear and even after changing the water the algae re-appears very quickly and
this happens even if you have a filter installed.
Green/brown cloudy water is normally caused by millions of algae remaining
suspended in the water. Each algae is about 4 microns in diameter (1 micron is 1
millionth of a metre or extremely small).
The reason why algae is not removed in many filters is due to its small size -
if the medium in your filter has gaps/pores greater than 4 microns in size then
the algae will just get re-circulated. By the way most filters suffer from this
design problem so do not think it is a problem with yours. It is almost
impossible to design to remove algae by filtration alone.
Algae growth is most common in ponds where conditions are most suited to their
requirements - lots of fish being fed lots of food, warm water as it is in
summer, and strong sunlight.
The waste products from fish eventually create nitrates in the water and most
pond food contains phosphates and lots of nitrogen. These are fertilisers for
plants, as you know from general gardening. Equally they are fertilisers for
algae - remember algae are plants.
If there was no nitrate and phosphate there could be no algae.
Even if there are no fish in the pond it is possible to get algae problems. This
is a common problem these days even in large waterways and is the result
of nitrate contamination of groundwater from the widespread use of fertilisers in
All tap water contains nitrates and in some areas probably phosphates. Also wind
blows debris into ponds and water features and this debris also contains these