I’m nuts about the importance of this subject and have written about it with updates in 2010/13/15/18 and now again for 2023.
So what’s the big deal about oxygen??? You have all seen many ponds and just about nobody ever says anything about oxygen or having oxygen problems – just that you need to have a waterfall or fountain or tower filter or air pump and run it 24/7. So get over it Koi Jack and move on – Well no, I just can’t and it is a significant issue in regards to your koi’s general health and development – BIG TIME. Yes, almost all ponds out there have sufficient oxygen levels to support koi survivability!!! They can live a few days in the 5ppm range and require at least 6ppm to maintain life sustaining functions. So you need to be at 6ppm or above or your koi would be dying. Again, what’s the big deal? Well to quote Recirculating Aquaculture Systems, “Of all the water quality parameters, dissolved oxygen is the most important and most critical parameter…” Now before you jump all over me for quoting the bible for raising fish for food and/or sale – their goal is to get the most growth and have the healthiest fish with the highest possible metabolism of food. If you want to achieve the best your koi have to offer – then I say the above quote is very relevant. To quote Christopher Neaves, L.R.S.M., “It is an undisputed fact that koi have better growth and better color in oxygen-rich environments.” I know I’m just a name dropper LOL.
SO what’s your pond temp?? We will soon have warmer weather and some hot weather later in the summer with some ponds if not all exceeding 77F and the oxygen carrying capacity of the water will be below 8mg/L (optimum level for koi) and could become an issue for your koi and your pond system. Understanding koi pond dynamics can be a bit complex with multiple variables that are both interwoven and interrelated. This subject would normally require several pages of text, but in an attempt to keep you reading and maybe to do some further research on your own I offer the following short story.
Your whole pond system is dependent on dissolved oxygen for survival! As noted earlier, koi need a minimum of 6ppm for low level expectations for growth and viability. However they can and will survive at lower levels reported at 5 and 4 ppm. (Note: 1ppm = 1mg/L) As pond water temp goes up its capacity to hold dissolved oxygen goes down: at 50F O2 saturation is about 11mg/L; at 68F O2 saturation is down to 8.6 mg/L; at 77F O2 saturation is down to 8mg/L; and at 86F O2 saturation is becoming seriously low at 7.4mg/L. These data are at sea level and are even lower as you rise in elevation. Each 1mg/L drop in oxygen is in fact a 12% reduction in available oxygen. Also, if you have salt in your pond then the capacity of the water to hold dissolved oxygen is further reduced. Now we need not forget that other parts of the pond system are also dependent on oxygen. “Biological filtration consumes about 5 milligrams of oxygen for every milligram of ammonia converted to nitrate” (Christopher Neaves, L.R.S.M.). Another 3 to 5 milligrams are estimated values towards oxygen used by other pond bacteria and microbes per milligram of converted ammonia. Simply put – over feeding overstocked ponds will produce increased levels of ammonia further reducing available pond levels of oxygen which is only exacerbated at higher water temps with less available dissolved oxygen to begin with. Did you know ammonia is more toxic at lower oxygen levels especially at the microenvironment of the gills (serious subject for another article)? Oh, and any organic waste (DOC) decomposing in the water column and on the bottom of the pond and filters requires oxygen to do so. And, let’s not forget that any plants and algae consume oxygen during dark hours. Algae blooms have been credited with using more oxygen at night than the koi in a well-stocked pond!!! Lower levels of oxygen will lead to higher levels of carbon dioxide levels which will drop the pond pH and you have the daily results of the lowest levels of oxygen being at day break. At 77F you can anticipate an hourly O2 requirement of around 250 mg for each kilogram of koi body weight (Advanced Koi Care – Saint-Erne, DMV). Yes, at the time when the biological oxygen demand of the system and our koi is at its highest requirement the water’s available dissolved oxygen levels are reduced. When O2 levels get low enough to have fish loss due to hypoxia, the BIG koi die first.
What to look for: koi become lethargic, reduced appetite, collect at the surface and at the waterfalls, dull or fading colors, gill damage (hyperplasia) which can lead to bacteria gill disease.
What to do: This is a looooong list but not limited to and not in any order of precedents:
Observe your koi’s behavior and are you happy with growth and color? (Both are said to be unquestionably improved in an environment rich in oxygen).
Test the water for O2 levels early AM and later evening. Meter or Box test kit.
Add air blower with stones or other available units.
I usually turned on my 40L air pump when the temp hit 74F with O2 at 7.6mg/L (early AM) and the air goes to the front end of my bio-chamber so it does not disturb my viewing of my koi in the pond. Don’t forget the difference between 7% oxygen and 8% oxygen is a whopping 12% more oxygen. (Chris Neaves)
Shade (big time)
Decrease pond turn- over time
Reduce fish load
Keep up with your regular pond maintenance and water changes (well water low on O2 usually)
Add a venturi (not below 20 inches)
Add a fountain
Reduce any existing salt level
Eliminate any algae bloom (UV)
Enlarge waterfall spillways making water column thinner when it goes over the edge
Anything to agitate the water at the surface
Look at tower filtration
Start planning your next koi pond
Now I got only two more things.
First: Why do any of the above? – I truly believe the less energy my koi expend meeting their daily oxygen demand the more energy they will have available to grow (length, girth and repair of body tissue), improve color and have a decreased incidence of illness and disease (healthier with less stress).
Last is sort of a disclaimer to keep in mind. As in most cases you can overdo it and be paying money for increased dissolved oxygen that is of NO consequence to the koi and at worst leads to gas bubbles. Other environmental conditions aside, oxygen levels above saturation in fresh water fish do not result in any additional oxygen carried by the blood. The gills can only transfer so much oxygen to the blood and each red blood cell can carry only so much oxygen.
My hypothesis is if they use less energy to get that max oxygen they are capable of carrying in their blood system then there is more energy available to fulfill to the maximum of what’s in their gene pool in association with the environment you provide for them to achieve that big smile on your face and pride in your heart when you look at or show your koi to friends or other koi hobbyists or, better yet, bring them to the next koi show.
Well, I just got started on this subject and did not do it justice. As always its content is from limited experience and lots of reading with most of the credit (this time) going to C. Neaves articles in Koi Ponds, Filters and Water and Advanced Koi Care by N. Saint-Erne.
Not sure why it’s just so easy to not be concerned about oxygen levels, when it is so important to the health and environment of our koi and our ponds??? I consider it important enough that my current oxygen meter is a Hanna H198198 Optical dissolved oxygen meter that runs about $1,500 but we all know how anal I can be about certain koi things LOL Be safe and healthy both you and your koi.