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The case for algae in koi carp ponds         (The case for algae in koi ponds)


Koi keepers usually dislike algae and do their best to eliminate it but is algae the menace that it’s normally portrayed as or does it have any benefits for koi or for the koi keeper?



Magnified view of spirulina

Spirulina 250

Spirulina grows as a dense mat

The case for algae in koi ponds

Of course algae is beneficial to koi, no question about it.  If that was not the case why on earth would koi keepers pay a premium for koi foods containing spirulina?

Spirulina (arthrospira maxima) is a fresh water blue-green alga, where cells are joined from end to end to form twisted filaments. The name spirulina comes from the word "spiral" because, under a microscope, it looks like a compressed spring.

Spirulina uses sunlight and water in a process called photosynthesis in order to manufacture the simple sugars that it needs to provide it with the energy and basic raw materials that it needs to grow. It is rich in carotenoids and is reputed to be one of the world's best natural colour enhancers for koi.

Spirulina’s main carotenoid ingredient is zeaxanthin which, when eaten, is converted by fish into astaxanthin, the red pigment needed for vibrant red colours.  Spirulina is easily cultivated where the water chemistry suits it but is very unlikely to be able to flourish in a koi pond because it needs a high pH and very high levels of carbonate or bicarbonate in the water.

Chlorella vulgaris02

Magnified view of chlorella vulgaris

A substitute we can grow in our ponds

Two common species of algae that grow naturally in koi ponds and which contain significant amounts of the astaxanthin pigment are chlorella vulgaris and haematococcus pluvialis which both are forms of planktonic (green water) algae.

Trials to investigate skin colour enhancement were conducted on groups of near identical koi as far as size and shape were concerned.  There were three varieties; showas, bekkos and a group that the researchers described as “predominantly red koi” and which were presumably benigoi.

The exact variety of the predominantly red koi isn’t clearly stated in the results because the researchers were scientists studying colour enhancement due to nutrition not experts in koi appreciation.

A dietary supplement from spirulina was compared with supplements from the two more common algae species; C. vulgaris and H. pluvialis. These natural colour enhancing supplements were also tested against a diet containing a synthetic colour enhancing additive (synthetic astaxanthin) and, for comparison, a control diet with no colouring added.  The five diets were fed to five separate groups of koi for 10 weeks.  Initial and final samples of skin from the dorsal area were taken.  They were all analysed for carotenoid content and a spectrographic analysis of the red hue.  The more effective colouring additive was found to be the supplement from the C. vulgaris which provided both maximum total carotenoid deposition and red hue for the showas studied and particularly for the benigoi group.

Testing the bekko with a carotenoid food was a control which would demonstrate any possible adverse effects such as a red tinge in the white ground.  When koi feed in green water they naturally ingest these types of planktonic algae cells and benefit from the axanthin they contain.

Nitrate spoils koi
Nitrate doesn’t only increase TDS readings unnecessarily, it also has consequences on the growth and quality of your koi.  It is often said that nitrate has a detrimental effect on the growth and the quality of a koi’s development but, until recently, this has only been spoken of in anecdotal terms.  In fact, although it doesn’t seem to be widely known, the research into the effects of nitrate has already been done. In the late ‘90s, Takayuki Izeki, writing on behalf of the ZNA research division, shared his observations on the effect of nitrate on the white ground of kohaku. He found that the maximum acceptable nitrate level for koi keeping should be 15 mg/L, saying: "anything more than this and the skin gradually begins to deteriorate but will improve again if the concentration is reduced."

He also said that if the nitrate parameter could be kept lower than 5 mg/L, "the skin becomes so white it virtually shines". He found that the negative effect of nitrate was caused by it reducing the koi’s ability to discharge metabolic toxins from the body which resulted in these metabolic wastes building up in the skin.  He also stated that an additional factor was due to the fact that nitrate reduced the amount of oxygen that could dissolve in pond water and that nitrate levels above 10 mg/L adversely affected oxygen dissolving into the water column to such an extent that there was a noticeable effect on koi growth, skin and colour development.  If a growing on pond is allowed to go green and develop a thriving colony of blanket weed it will significantly reduce the nitrate level of the water.

Cultivation of algae is very easy and they multiply extremely quickly. All they need to grow is light, water and carbon dioxide, plus a little phosphate, nitrate and other minerals.  The photosynthesis process by which they convert carbon dioxide in the water into oxygen can be simply stated as:

6CO2 +  6H2O (+ light energy)   ==>    C6H12O6 +  6O2

Carbon dioxide + water (plus energy from light) becomes glucose + oxygen

Plants 105This basic equation says that, when light shines on plant or algae cells, six molecules of carbon dioxide plus six molecules of water are combined to make one molecule of a basic form of sugar called glucose and six molecules of oxygen.

The plant or algae uses the glucose as a building block to make more cells in order to grow and the oxygen is released as a waste product. Photosynthesis is essential for all life that breathes oxygen, and oxygenating the water is often thought to be the only advantage that is brought to the aquatic environment by algae.  However photosynthesis is only part of what is happening as algae grows.  The biochemistry inside an alga cell is far more complicated than that.

There are many simultaneous processes happening as algae grows.  These processes produce a variety of colour pigments, vitamins, essential fatty acids and amino acids, even antibiotics.   H. pluvialis is the richest known natural source of the red colour pigment astaxanthin. In green water, koi can obtain all these benefits by simply swallowing these planktonic algae cells as they eat other foods.

Algae is not only green, it’s green
The varying costs of payment plans for electricity make it impossible to make a definite rule about the running costs of electrical equipment but there is a rule of thumb that, at the time of writing, (2014), gives a good approximation for costs in the UK. This is to assume that a piece of electrical equipment costs about £1 per year per watt to run. Using this approximation for a typical 55 watt ultra violet clarifier shows the running cost for a year is around £55 and there will be about another £20 per year in replacement lamps. This isn’t really a great saving for the koi keeper but, by switching off a clarifier on a growing on pond, the koi will not only benefit from the advantages of the green water but the carbon footprint of the pond will be reduced a little as well.  Green water makes for a green environment!

Green water is better than chemical warfare
Algae are single cell plants that can be thought of as balloons half filled with “algae juice”.  The walls of these little balloons are made from compounds called polysaccharides. Common bacteria have cell walls made of a similar compound, peptidoglycan, which is another form of polysaccharide.

The way in which some blanket weed killers work is to release enzymes that make little holes in the polysaccharide walls of the algae balloons so that the internal fluids leak out and they effectively bleed to death. But if bacterial cell walls are made of similar compounds, it seems reasonable that these must also be affected. Where low doses are used and the biofilter is at peak efficiency, the bugs can multiply quickly enough to make up for the damage caused but there are repeated anecdotes of biofilters dying after a blanket weed treatment.  Chemical warfare on blanket weed may damage your biofilter.

Chemical warfareTwo other common ingredients in algae treatments and preventative products are copper and/or zinc. These may be either the main active ingredients or they may be added to supplement other ingredients such as enzymes. There are also electronic devices on the market that put copper into the water.

The treatments and electronic devices that put copper or zinc into the water often have that fact disguised by referring to them only as “natural minerals” in order to make them seem fish friendly and natural in the koi environment when really what these treatments or devices are doing is conducting chemical warfare on algae.

Copper or zinc have no place in koi ponds, even in very low doses, they slowly accumulate in fish tissues and poison them. Copper is also very effective at killing biofilters.  Often the damage being done by this poison to the surface “layers” of the biofilm which experience the full effects is offset by the rate at which the bugs deeper down in the biofilm are multiplying.  The deeper down bugs can continue to replace their dying cousins nearer to the surface because the biofilm gives them some protection from the full effects so it often appears that the colony, as a whole, hasn’t been affected. However, this isn’t always the case and sometimes they can’t keep up with the death rate that is going on nearer to the top.  The consequences are that the biofilm slowly dies as the top “layers” are killed and the poison reaches those that previously were protected

I personally would rather have a pond with the clarity of pea soup than risk the consequences of putting copper or zinc into it.

Ponds don’t have to be either completely green or clinically sterile.  There are other options.  Given a choice, koi would prefer the former whilst most koi keepers will prefer clear water. Growing on ponds should be allowed to go green but, for a display pond, it’s possible to have a compromise where both the hobbyist and their koi will be happy; clear water with a limited growth of algae on the walls.

A suitably sized UV clarifier will solve the problem of green water for those who want crystal clarity although, even with this arrangement, there are options available.

Clarifiers can be put on a timer so that the degree of clarifying can be reduced in order to allow a green tinge to develop which will benefit the koi in advance of a koi show or they can be turn off whilst the koi keeper is away on holiday.  The clarifier could then be returned to full 24 hour use afterwards and the water will return to full clarity in a day or two.

A green pond or green candy floss?
Algae provides such a range of benefits in terms of colour enhancement, growth, nutrients and improving skin quality by reducing nitrate levels that the case for green water and blanket weed in growing on ponds is proven – no question about it!

What about the case for algae in the main pond?  There seems little point in buying good quality koi and putting them into a green pond where they can’t be seen, but algae has such benefits that maybe there is room for compromise. Ultra violet clarifiers will keep a pond free from green water but is it necessary to completely annihilate every trace of nutritious algae? Chemical warfare on blanket weed may well mean that any residual traces contain substances such as copper or other chemicals that are undesirable in the koi’s diet.

A koi browsing on blanket weed that hasn’t completely died back after the treatment will be taking in any copper or zinc that the cells have absorbed. Allowing some blanket weed to grow and removing the excess by the old method of twirling it on a stick to make green candy floss may be the best compromise between a natural beneficial food and an excess of blanket weed.


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