How do you know if your pond needs more oxygen?

[jjohnwm]

...by the time fish are surfacing, oxygen has likely been low for hours.

I'd love to hear an explanation for this ^ statement, because it just doesn't sound reasonable. Oxygen is required constantly, and I would expect the lack of it to become apparent almost immediately. It isn't analogous to poor nutrition, which causes problems that gradually come to light over weeks or months. A lack of sufficient oxygen will affect an organism immediately, right now! Fish removed from a well-aerated, well-oxygenated aquarium and placed into a bucket for temporary confinement or perhaps transfer, can if overcrowded and/or overheated begin gasping at the surface within a very short time...certainly not "hours".

I would suspect that part of the problem is that old bugaboo: overcrowding. Personally, I keep my fish in lightly stocked tanks and ponds, such that a power outage is not immediately followed by fish deaths due to lack of oxygen. Aquarists today always seem to need one more fish...and this results in crowded aquaria that are totally dependent upon artificial means of aeration, filtration and other forms of water management. Then, when these artificial methods are interrupted, disaster ensues.

Referring to ponds raises another question: what exactly is meant by a "pond"? People smugly talk about "growing out" fish in an aquarium and then moving them into a pond when they are large. Then they show a picture of the "pond"...and it's a puddle that can be stepped across easily, or a small kiddie wading pool better suited to bathing a dog. Calling a container holding X gallons of water by the grandiose term "pond" does not confer magical fish-keeping qualities upon it. It's still X gallons of water.

My single small outdoor pond is a cavity dug into the earth, waterproofed with an EPDM liner...and that's it. It has a light stocking of fish, a heavy growth of plants...submerged, floating and emersed...and a maximum depth of perhaps 36 inches in the center. I have toyed with a cheap solar-powered pump which did not last long, but that was strictly an experiment in aesthetics. The fish have never displayed any apparent signs of oxygen deprivation. In any case, the pump only functioned during sunlight hours, whereas all those evil oxygen-consuming plants engaged in their heinous activity during darkness, reverting to producing oxygen rather than consuming it before the pump ever got going in the morning...just as they do in nature...

Being an inground pond, mine has its temperature buffered and moderated by the surrounding earth. It will never warm up to the point where oxygen becomes a concern, at least not with the stocking it has. In fact, the calm water...which the worryworts among us would characterize as "stagnant"...is several degrees cooler at the bottom than it is at surface, and during hot weather the fish tend to stay in the depths. They make periodic feeding sortees to the surface but spend most of their time deeper...just as they do in nature...

Contrast that to an above ground "pond" like the several stocktanks in which I raise fish outdoors during the warm months. These tanks are also "stagnant", and while they undergo temperature stratification, they do not have the protection afforded by being dug into the ground. Surface temperatures can rise far higher than the inground pond ever experiences. Warm water extends deeper down, and in any case they are only around 22 inches in depth. Water temperatures in even an 8-foot round tank can vary as much as 12-15 Fahrenheit degrees in the course of 24 hours. These tanks are also heavily planted and lightly stocked, but they are much closer to the edge of disaster at any given time. They require shading from the afternoon sun during the height of summer...and I'm talking about summer in Manitoba, not California or Florida.

Fish behave in these tanks the same way they do in the dug pond; they spend time near the bottom during the hottest periods, approaching the surface in mornings and evenings...much like they would do in nature. No gasping, no distress.

Aeration added to these tanks must be approached very carefully. Simply tossing in an airstone or a sponge filter...as I originally planned to do...can lead to disaster. Destratifying the water with aeration produces a uniform temperature throughout, top to bottom, and that temperature can be far too high at midday in full sun. I have had problems with several species that simply could not do well at these temps, which can approach or exceed 80F easily and sometimes hit 90F. As non-intuitive as this may sound...the only solution is to discontinue aeration and circulation and allow the water to stratify again by temperature, allowing the fish to find their comfort level...much as they do in...well, you know.

Oxygen dissolves in water naturally; aeration will obviously increase the speed at which this can occur, but there is much calm water in nature that is full of healthy fish. How can that be?

If you love gadgets and tech then you can play with it all you want, and it can absolutely improve aspects of fishkeeping...but that doesn't mean it's necessary, nor even always desirable. If a reliance on tech support encourages you to create an unnatural overcrowded system that falls apart when the power goes down... that's not a good thing.

 

[danotaylor]

Summer: higher oxygen demand, so stronger or longer aeration

Oxygen demand is relative to metabolic processes in living organism. Temperate of the environment relates to availability not demand. The warmer the water the less O2 carrying capacity it has, resulting in a lower DO level.
What jjohnwm said about pond style and temperature fluctuations has tremendous relevance in figuring out each individual pond scenario.
The more biological processes, including waste breakdown, and consumption by algae which is more prevalent in warmer months, results in a further decrease in availability.
What am saying is that as the pond water warms in the summer O2 consumption increases reducing already lower DO levels d/t reduced O2 carrying capacity of warmer water.
Constant surface agitation together w waste removal will help maintain sufficient O2 levels in a pond <3’ deep. In deep ponds it is dependent on the amount of rotting waste in a static water volume as to what and how to achieve biological stability.
If you search “Inspired By Nature”, a natural pond management company that operates out of Ohio, there loads of great, science based, data on this subject

 

[jjohnwm]

Good points ^ about oxygen demand vs. availability. The focus of this thread seemed to be on fluctuations throughout each day; mention was made of fish displaying distress in the morning, suggesting that the oxygen consumed during darkness by algae and higher plants dropped the overall oxygen levels below what the fish needed. Posters refer to having observed this multiple times; assuming that at least some of those posters are human beings and not bots, I guess this can be a concern.

While the plants produce oxygen during the day, the fish are most active and require the most oxygen at those times as well. At night, the plants revert to using oxygen...but most fish are at their lowest ebb in activity, so their utilization is reduced to its minimum levels as well. Of course, some predators are most active after dark...and many of those are air-breathers like many cats, lungfish, etc. so perhaps this is an evolutionary response to those horrid "stagnant" waters that are so creepy, but maybe it's also an adaptation to facilitate activity when the water's oxygen content is lower?

Another thing to consider is that shallower and smaller bodies of water...like our pitiful "ponds"...will exhibit greater temperature swings more quickly. The large changes I mentioned in my earlier post...cooler at night, warmer at midday...would also work to increase the oxygen-carrying capacity of the water after dark, when the oxygen production by plants has reversed to consumption. So we have fish competing with plants for the oxygen that is present after dark...but fortunately the oxygen carrying capacity of the cooler water is greater and the lower activity level of the fish decreases their need. Fortunate coincidences abounding. You'd almost think that the whole system evolved to work that way.

Oxygen requirements will vary from species to species, of course, and it's reasonable to infer that demand will be greatest when the fish are kept at the optimum temperatures for their species since they will then be most active. I don't think it's coincidental that Goldfish and Koi have been bred for centuries; as a species they are active and able to remain healthy over a very wide range of temperatures. I can put Goldfish outdoors at least a month before "tropicals" and leave them out at least a month longer in the fall.

They're not adaptable and easy to keep because they have been bred in captivity for so long; rather, they have been kept for so long because they are adaptable and easy to keep. Mine will display breeding activity as soon as water temperatures reach around 60F in my basement, and they continue to breed like mice after they are taken outdoors and send the summer living in a "stagnant" weed-filled pond. The only time they are seen "gasping" at the surface is when they are competing to hoover up the pellets I occasionally provide as food...and those feeding frenzies are equally enthusiastic whether the pond is at 60F or 85F. All without artificial aeration, circulation or filtration.

Don't these dang fish know they should be choking, suffocating, gasping their last? I'd better not let them read this thread, it'll scare 'em to death. Ignorance is bliss...and I tend to trust what I see with my own two eyes in the stock tanks and ponds in my back yard, as opposed to what I see on the internet.

 

[danotaylor]

Fair comment about personal observation for sure.

Fortunate coincidences of evolution…hmmm….not sure about that personally. Seems like more of an intentional design feature to me

On the OP’s other thread regarding pond related questions I requested info on geographic location (seasonal temp variations) pond size, surface area, depth and proposed or actual stocking. All of these data points are essential to work out the answer to send questions. Otherwise information being offered is very general and nonspecific to the question.

I did suggest checking out Inspired by Nature’s website as the bloke who runs the company has been successfully managing ponds over a considerable period of time. The info on his site has been time tested & proven in his business practice, the longevity of which is a testament in itself to his long management practices