Water Gardening & Fish Pond Keeping Is Also About Water Quality Management
You look into your perfectly clean and clear pond, you see fish darting around,
they come to your hand to feed having lived happily in their home for well over
2 years. The plants are growing well and you are pleased with your investment
and especially that you have never lost a fish. This desirable situation is made all the more possible when you understand
something about water quality and what is happening in a pond.
The fundamental and single most important factor behind good water quality is
excellent biofiltration. Poor filtration will undoubtedly create poor water
conditions that in turn will result in water looking poor, fish disease and
possibly even fish deaths. There are specific parameters that indicate good or not so good water quality.
Water Quality More Advanced Considerations
The following parameters are important in good pond keeping in addition to the
absolute need for biological filtration:
High levels of oxygen
Low variations in pH of the water
Good levels of carbonate hardness
The absence of pathogenic bacteria
The Vital Importance of Oxygen
On top of Everest we cannot breath without
assistance. Fish are like that and so are bacteria. Starve them of oxygen and they suffer
just like us.
Top class koi ponds and filters literally bubble with air which is continuously
pumped into the circulating water, the filter and the waterfall, as well as the
pond 24 hours a day 365 days a year. There are some things you really do need to know about what happens to the
oxygen concentration in your pond under different conditions. In this short
discussion weI will state matters factually and illustrate by numbers where
Water can hold less oxygen the higher the temperature rise in the water.
This means that in July and August (Northern Hemisphere mid Summer) there is
much less oxygen in a pond than in January when the water is much colder. This is why trout
need cold water - they need high levels of oxygen that they cannot get in warm
water. Koi and goldfish would thrive on 4ppm levels dissolved in water whilst
trout need 20% more (5 ppm).
Oxygen is introduced to water at the pond surface and by any mechanical means
such as use of a fountain, waterfall or air pump. Aquatic plants also play a
At 10 deg C (50 degrees Fahrenheit) at sea level water can hold 10.9 mg/litre of
oxygen. At 20 deg C it can only hold 8.8 mg/litre and at 30 deg C the saturation
level is 7.5 mg/litre. Don't worry too much about the actual number just focus
on the significant reductions.
In practice few systems reach these saturation
levels and this is the reason serious koi keepers blow
massive amounts of air into their ponds and filters in order
to get as close as possible to saturation.
Plants are always a good idea in a pond because they introduce oxygen into the
water during the daytime parts of the 24 hour daily photosynthesis cycle. At night the plants reverse this process by using up oxygen from the water and
converting it to carbon dioxide and then to carbonic acid.
This is another reason for maintaining pump flow 24 hours per day so that
circulating water continues to pick up oxygen and distribute it throughout the
pond during this night time period.
We have previously made the point that in ponds where
high levels of algae
existed then these algae could totally deplete a pond of oxygen overnight
causing fish loss. Large fish tend to suffer first.
In summary you cannot overdo the introduction of air into a pond.