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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 possible.

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 role here.

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.


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