Q: At various times this summer I have seen my Koi gasping at the
pond surface and around my waterfall. Does this mean that there is
not enough oxygen in the pond? Is this because of exceptionally high
temperatures or for some other reason? I have a waterfall and a
Blagdon air pump with two airstones; my pond is 3,500 gallons. Do I
need more aeration than this? What can I do to prevent this
happening in the future? If this is due to a lack of oxygen, will
this do any damage to the health of my Koi?
A: Thanks for your letter which details your koi-watching
observations, and provides your own helpful suggestions as to the
cause of your gasping koi. Understandably, you may be surprised by
an apparent DO (dissolved oxygen) deficit as you are already adding
supplementary oxygen via aeration and a waterfall. What I find even
more surprising is that you have experienced sufficiently hot
weather this summer to cause a low DO problem in the first place!
Let's explore....
Does this mean that there is not enough oxygen?
Before being able to confirm whether your pond is sufficiently
aerated during hot weather, it is first worth considering other
factors that could lead to similar gasping behaviour in your koi.
Nitrite:
Besides a drop in DO (which is the most likely cause of
the gasping behaviour you have observed) another cause could be that
your koi are suffering from poor water quality, specifically nitrite
toxicity.
If for some reason, toxic nitrite is not being broken down and
detoxified effectively by your biofilter, then it will cause a build
up of nitrite in your pond water and then subsequently within your
koi's blood and tissues. When nitrite reacts with the
oxygen-carrying haemoglobin within the blood, it forms a stable
non-oxygen carrying form of haemoglobin, which will in turn cause
your koi to gasp.
For this reason, the next time you observe your koi gasping (I hope
you don't once you've read this reply), it would be prudent to carry
out a water test to eliminate nitrite as the cause.
Medication ...
Another factor to investigate and eliminate is pond medication. Some
pond medications when added to the water can cause quite a severe
drop in DO through chemical reaction. Medication may also reduce DO
through adverse interaction with other pond life. Extra aeration
should be added during any course of treatment as a precaution and
particular care should be taken after the use of an algicide. Dead
algal matter will put an extra burden on the oxygen budget within
the pond as it is broken down by bacteria. Have you been using any
medications periodically that may have preceded any gasping
incidents? If not, then you can eliminate medications as a possible
cause.
Is this because of exceptionally high temperatures or for some other
reason?
Hot Weather: Your low DO prime suspect.
Oxygen behaves in a surprising way (compared to other solutes, such
as salt) in that as the water temperature rises, its ability to
dissolve oxygen reduces. Compare this to salt (which dissolves
better in warm water) and you can start to appreciate the unusual
relationship water has with oxygen. So as water warms up, its
ability to hold DO decreases and yet your koi's oxygen requirements
increase. The DO requirements of other organisms in your pond such
as bacteria and other organisms will also increase.
If your pond had been running close to a limiting oxygen level prior
to each hot spell then when the water temperature rose, the 'double
whammy' effect of both pond organisms demanding more oxygen and your
pond water holding less DO would have left your koi and pond
environment in an oxygen-deficit.
....some other reason
Dawn depletion is another factor besides high temperature can cause
DO to drop so low that it will cause your koi to gasp. In a natural
planted pond, full sunlight is a real asset as a natural source of
oxygen as the plants (and algae) produce far more oxygen via
photosynthesis than they use in respiration. However, at night, the
same plants will still be using oxygen and will not be releasing any
oxygen through photosynthesis. This will cause a drop in pond DO
causing the fish to gasp first thing in the morning as a result of a
phenomenon called dawn depletion. A remedy for this is to thin out
excessive submerged plant growth and improve aeration or circulation
within the pond.
But as you observe your koi to be gasping in hot weather (mid
afternoon, then this is an unlikely cause - but nevertheless, worth
keeping an eye on.
Do I need more aeration than I currently have?
If warm weather seems to be tipping your pond's DO budget over the
edge, you need to consider whether your pond is receiving sufficient
oxygen to allow the complete array of organisms to respire
efficiently, recognising that for your mature pond to remain
balanced, all contributory organisms must be able to function
healthily. Furthermore, focussing on the koi themselves, your pond
is supporting diverse populations of micro organisms (that are in
turn, sustaining your koi's environment) and if oxygen becomes
limiting, will lead to a deterioration in your water quality and koi
health
All organisms that respire aerobically require oxygen. This includes
heterotrophic bacteria that breakdown organic matter (and
autotrophic bacteria that use oxygen during their release of energy
from inorganic compounds such as ammonia and nitrite), fungi,
protozoan organisms that scavenge the pond for debris and larger
metazoan organisms that will filter and graze on organic material.
Plants too respire constantly throughout the day and night, which
includes, of course blanketweed (if you consider your pond to be
unplanted) and any other algae adhered to pond sides and pipework,
as well as any larger aquatic plants that may be found within a
planted pond. All of these vital organisms rely on a supply of
oxygen, just as a burning fire does to keep it functioning
effectively. Deny them oxygen, and the water quality will
deteriorate; add extra and the pond will roar into life, just as a
bonfire does in a gust of wind.
I am a little concerned that the existing arrangement of airstones
and a waterfall is not sufficient for your pond. This leads me to
question whether the stocking and/or feeding levels are both too
high for your pond. It is difficult to give specific advice on how
many koi should be kept in a 3500 gallon pond so I would double
check by asking other pond and koi keepers to visit your pond and to
verify its stocking density.
If having eliminated all other causes of a low DO you are able to
conclude that the warm weather is the sole cause, then you need to
look at adding extra aeration.
You could try to see if your existing air pump can be used to
make the necessary improvements
Having recognised that your koi are in competition with other pond
organisms for oxygen, add a few more airstones to your biochamber.
This will provide the extra aeration where it is needed, leaving
more available for your koi. Research has shown that the most
efficient aeration is achieved from the pond bottom using a
fine-bubble diffuser. Try additional air stones at first (if nothing
else, to check that your existing air pump can pump down to the pond
bottom). If you are not so happy with additional trailing airlines
into your pond then I suggest you consider a single airdome (which
can be fitted onto a bottom drain, hiding your airline within the
waste pipe. Compared to airstones, air domes produce a greater
number of finer bubbles.
If this is due to a lack of oxygen, will this do any damage to the
health of my koi?
DO levels that are sufficient to cause your koi to gasp will cause
you koi problems both directly and indirectly.
Direct:
Koi will be stressed by both acute and chromic incidences of low DO.
The gasping response is a koi's method of accessing oxygen directly
from the atmosphere (because the DO levels cannot supply their
need). This is a short term strategy as it cannot be sustained
indefinitely as CO2 levels will increase further in the blood and
oxygen levels will fall until they become critical to the life of
the koi. The usual hormonal response associated with a stress-event
will be released, making koi more susceptible to pathogens.
Indirect:
Without oxygen, filter bacteria cannot oxidise (and detoxify)
ammonia into nitrite and then into nitrate, making these toxins
accumulate in the pond. If a pond or filter are allowed to become
oxygen deficient for an extended period of time, anaerobic
conditions will prevail causing unstable water conditions and the
tell-tale bad-egg smell. This will adversely affect water quality
and stability which in turn will jeopardise koi health.
In conclusion, on the face of it, your low DO problem should be
easily rectifiable, perhaps even using your existing air pump.
Double check that you are not trying to achieve the impossible by
overstocking and overfeeding your koi, otherwise your pond will be
very vulnerable should your supplementary aeration ever break down.
How to oxygenate your pond
- Diffused Oxygen - Fine bubble from the pond bottom. Wet biochambers will also benefit from strategically placed diffusers.
- Venturi - Most easily installed through the pond wall from a
final filter chamber. Look impressive but only really aerate the
upper layers of water
- Moving water: Waterfalls and fountains. The energetic water
movement mixes oxygen into the water, helped by the constantly
moving water/air interface.
- Oxygenating plants. Not appropriate in a koi pond, but this is
nature's way and has been working in natural water bodies for
millennia. Beware of the risk of dawn depletion. If you've got
blanketweed in your pond, you will be benefiting from oxygen
released in the day.
How to avoid low oxygen concentration
- Treat aeration like filtration and always install more than the
stated 'text book' requirement.
- Do not overstock with koi
- Do not over feed or offer excessive amounts of food in warmer
weather
- When designing and building a pond, ensure that it has a favourable surface area to volume ratio
Ensure mechanical chambers are cleaned regularly
How to test for dissolved oxygen
I prefer to:
- Over-aerate
- Regularly koi-watch to spot any subtle changes in behaviour
To confirm you have sufficient DO, use a DO test kit or meter. You
should be aiming for 3-6mg/l. The test kit is a colormetric test
that will intensify in relation to the concentration of oxygen in
the water.
pond oxygen-carrying koi water organisms aeration
nitrite gasping weather medication "air pump" plants health reason
"high temperatures"
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