I'll give a shot.
Secondary to Oxygen, temperature is the most important parameter in any pond that supports life.
In a separate thread, Dave54 commented on the abrupt drop in air temps in his area of the UK and extolled the comfort to be found in his warm bed. Dave54 was reacting to 'stress' caused by this temperature change. Even without the warm bed, he has the ability to fairly quickly adapt to such temperature changes because being a human, he is warm-blooded. Which means that his body has the ability to generate internal heat by controlling its metabolic rate. Fish, on the other hand, are cold-blooded and lack this ability to control body temperature. Their metabolic rate and , as a result, all of their other bodily functions are directly regulated by the temperature of the surrounding water. The fact that humans are warm-blooded gives them somewhat of a built-in shock absorber when it relates to temperature change. Again, fish do not have this advantage. Any abrupt change in temperature, higher or lower, will impart stress to a fish. The greater the change in temperature, the greater the level of stress. Fish do have the ability to adapt/adjust to abrupt changes The adjustment period may take several hours to several days depending on the size of the change. In the case of extreme change, mortality is the usual outcome.
What is the temperature differential that may cause major stress in fish? Well, it depends on several factors....specie of fish, age of the fish, current health of the fish, extant levels of other water quality parameters. In one study It was shown that an abrupt change of 10 degrees Fahrenheit causes noticeable levels of Ammonia autointoxication in Carp/Koi.
Abrupt changes in pH also presents problems. More toxic Ammonia is present in water as pH and/or temperature rises. In performing a water change, if there is an overall increase in pH AND temperature , besides the fish being unable to expel Ammonia, they are exposed to higher levels.
Studies have been conducted on the ability of Carp/Koi to adapt to changes in pH. Assuming all other water parameters are the same, carp/Koi can adapt/adjust to any change within the pH range of 6.5 - 8.5. If however, the change in pH exceeds either the lower or higher limit of this range, mortality is likely.
In summary, major abrupt changes in any water quality parameter rarely occur in a natural setting. Those that do occur naturally are weather-related and seasonal. Fish have the ability to adapt/adjust to these changes albeit very slowly. Although there are naturally occurring weather phenomena, such as tropical cyclones, that cause such abrupt and major parameter changes, fish just do not have the ability to survive and massive fish kills occur.
So when performing a water change, it is extremely important that the pH and the temperature of both the pond and the source water be as close to the same as is practical. If this is not possible, then any major water change should be avoided. A little common sense goes a long way.
I totally agree with you on this meyer and quoted a problem with large waterchanges especially when ammonia and nitrates are present in large quantities in that there may well be problems afterwards with what is known as Ph crash though my source book Diseases of Carp and Other Cyprinid Fishes ISBN 0852382529 was quoting aquarium as an example, however the same may happen in the pond if things are not done in a correct way.
Interestingly one of the authors and Fish Science lecturer was a former member of our very own society here in Plymouth one I. wellby who again interestingly nominated us for our inclusion into the Koi magazines hall of fame 2009. He was by doing that thanking us for the love and attention to detail we gave our koi that was part instumental in him choosing his career .
As you can imagine we of the Plymouth society are quite proud of his achievements in life .
As to your mention of abrubt natural changes I warm against it from time to time and have done so on this very forum .
I believe this may be the paper in question that you are talking about ? :-
Catastrophic Oxygen Depletion Koi pond in your
We are grateful to the dedicated professors and researchers at our universities for their contributions to aquaculture. Because of their hard work and attention to detail, they have given us the information we need to keep our koi ponds and pond fish healthy, so we can enjoy the wonderful past time of pond keeping.
Catastrophic Oxygen Depletion and How to Avoid It
The Indiana ADDL is located on the Purdue Campus in West Lafayette, Indiana.
by: Tim Muench, DVM, MS
Edited by: Randy White,DVM, PhD
During the warm spring and summer months, we receive an increased number of phone calls regarding sudden fish kills in ponds. The typical history includes observing a very large number of fish dead in an otherwise normal pond following a rainstorm or summer thunderstorm. Usually the owner is very concerned that the fish may have died due to "run-off" of farm chemicals into the pond. Most of the time, these fish kills are a result of a phenomenon known as "pond stratification." Pond stratification is somewhat of a misnomer, since the stratification can also occur in lakes, creeks and some rivers. The stratification leads to a catastrophic depletion of oxygen which almost always results in a very high mortality of aquatic animal life within 24-48 hours following the "de-stratification."
The scientific reasoning behind this phenomenon of pond stratification relates to the temperature of the pond. In the early spring, while the temperature of the pond is still relatively low, the dissolved oxygen is uniformly distributed throughout the pond. As the atmospheric temperature increases, the pond begins to stratify, that is, become layered, with the surface water becoming warmer and lighter while the cooler and denser water forms a layer underneath. Circulation of the colder bottom water is prevented because of the difference in densities between the two layers of water. Dissolved oxygen levels decrease in the bottom layer since photosynthesis and contact with the air is reduced. The already low oxygen levels are further reduced through the decomposition of waste products, which settle to the pond bottom. After a rain, or any other event which disrupts the two layers, a "de-stratification" or "turn-over" of the pond occurs. This has the effect of releasing all of the dissolved oxygen from the upper layer of the pond into the atmosphere, hence, a catastrophic oxygen depletion.
Once stratification of a pond occurs, there is nothing that can be done to alleviate the situation. However, pond stratification can be very easily prevented by the use of supplemental aeration. Aerators come in all sizes and shapes as well as different power sources, i.e., tractor p-t-o, electrical, mechanical, etc. It is important to aerate the pond properly, i.e. match the size of the aerator to the pond, since over-aeration is wasted and may even lead to oxygen supersaturation, known as "gas-bubble" disease and under-aeration will not prevent stratification.
In those cases where we suspect catastrophic oxygen depletion, all other possible pathogens including bacterial, viral, parasitic agents are eleminated from the differential diagnosis list. However, the history of several days to weeks of warm weather followed by a sudden rainstorm are highly suggestive of this condition. If you suspect that you are dealing with a pond turn-over situation following pond stratification, it is imperative to have the pond owner take a water sample and have the dissolved oxygen (DO) concentration evaluated immediately. This water sample should be collected in a clean glass jar or bottle with a screw-top lid and should be completely filled by completely submersing the sample and container and placing the lid on the container while it is still under water.
By: Tim Muench, DVM, MS
Edited by: Randy White,DVM, PhD
Personally Priscilla you have in place a water change regiem of 50% which is more than enough.
We do a weekly water change of 40% using the trickle method of delivery via a dechlorination unit..
During the summer temeperature matching is quite an easy thing to do , we use an infrared thermometer to do so and this is just to back up the remote pond thermometer just to get it correct.
However the water change routine carries on throughout our wintermonths and there is a big difference in water temperature coming through the pipes, if done correctly by use of the very same trickle method then the ambient temperature of the ponds water will take up the slack with no noticable change in pond temperature perhaps only 0.2c - 0.4c give or takem, as such the koi suffer no stress throughout this change .
Its something weve done for th last 5 years of our 27 year hobby since we left the large indoor aquarium for the pond.
As meyer says a little common sense goes along way in our hobby and is what keeps fish alive and well our remaining 27 year old koi can attest to that I believe .