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DO or Dissolved Oxygen in detail..

DO is dissolved oxygen and yes, you can measure it!

Nigel Caddock NI

So why do you suppose that every year so many Koi keepers still get into trouble due to basic oxygen depletion? As one of the most basic and simple elements its often taken for granted. Be honest when was the last time you measured the O2 levels in your system?

Sure you check ammonia, nitrite, pH but how often oxygen? Up to a few years ago there was a reasonable excuse simply because of the lack of availability of affordable and effective O2 test equipment. Tetra changed that ten years ago with the introduction of their ground breaking O2 test kit with their popular and familiar reagent format and since many manufacturers have piled in including more recently of a range of digital readers.

Today there is no reason or excuse not to check your DO, its simple and inexpensive. Its also our view that of all water parameters dissolved oxygen in the most important single element, before pH, before ammonia before nitrate!

Its not hard to see that not only is it more difficult for warmer water to absorb oxygen, but it dissipates faster. Thats the basic reason that summer ponds are more susceptible to oxygen depletion. Throw into the mix atmospheric factors, humid sultry weather which compound pressure on the vital DO and what you have is a problem waiting to turn into a disaster. If you have relatively high stocking levels - you just lit the blue touch paper!!

Consider too that at elevated temperatures Koi respiration rates increase with activity and oxygen demand from your vital filter bacteria who are also in turbo mode, also increases significantly so the danger zone increases still further.

Whats it measured in?

Often numbers quoted in relation to acceptable levels of oxygen have been referred to in parts per million (ppm) 6 being the magic number. Problem is that all the published data and recommendations refer to salmon trout or other farmed fish. Its our unequivocal contention that these have little to do with Koi. Over the years NI has gathered information and data from many many sources and have formulated Koi specific data. The numbers, included later in this article, are offered specifically in this context and we make no claims that they are in any way definitive, they are however based on more than 20 years cumulative experience - all gained the hard way.

Dissolved oxygen is appropriately expressed in milligrams per millilitre. The table indicates the vital relationship between DO saturation and water temperature. This relationship is defining and needs to be carefully considered at all times. To give you an example DO saturation at a water temperature of 5˚C is 12.8mg per litre and when the temperature is 25˚C saturation its 8.4mg.

Do you know your DO levels?

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