The pH of water is important, not only to Fish, but to all aquatic life because pH affects the ability of fish and other aquatic organisms to regulate basic life-sustaining processes, primarily the exchanges of respiratory gasses and salts with the water in which they live. Inability to adequately regulate these processes can result in numerous non-lethal effects and even mortality, in cases when pH exceeds the normal range physiologically tolerated by aquatic organisms.
Unfortunately, there is no definitive pH range that is safe for all aquatic organisms. The acceptable pH range for aquatic life, especially fish, is dependent on other factors, including, but not limited to, prior pH acclimatization, water temperature, and dissolved Oxygen levels.
Our focus is the adaptability of Carp (Koi). Let’s look at some limits that have been determined by various studies.
-The lower pH limit for Carp (Koi) is between 5.0 and 5.5. Below this mortality occurs.
-The growth rate of Carp (Koi) is reduced at pH levels of 5.5 to 6.0.
-At pH levels of 8.0 to 8.5, the motility of Carp (Koi) sperm is reduced, thusly affecting the spawning process.
-Carp (Koi0 avoid pH levels of 9.0 to 9.5 (Goldfish avoid levels of 8.5 to 9.0).
-Carp (Koi) cannot survive at pH levels over 11.0.
-Carp (Koi) lose the ability to absorb Oxygen as pH decreases, with this becoming increasingly more severe at pH levels below 6.5.
We can see, as a result, that Carp (Koi) can survive in a pH range of 5.5 to 11.0. This may be the survival range, but is definitely not what we have termed a ‘Comfort Zone”.
The consensus of all examined sources would indicate that this pH ‘Comfort Zone’ is 6.5 to 8.5. This is further substantiated by the results of a test that showed that Carp (Koi) could be moved between different pH levels without any chronic effects as long as both pH levels fell within this range of 6.5 to 8.5. Any effects that were caused were temporary and non-lethal with the fish adapting and returning to normal within a short time. However, if the fish were transferred to a pH outside of this range from any level within this range, chronic effects or mortality usually occurred. In other words, Carp (Koi) will adapt to a sudden pH change of 6.5 to 8.0, but will suffer permanent physiological damage and even death if suddenly transferred from 8.5 to 9.0. They can adapt to changes outside of the ‘Comfort Zone’ when these changes are gradual This is evident in the fact that they are subject to diurnal fluctuations in pH in their natural environs, with the lowest being at dawn and the highest being in late afternoon, either or both of these levels being outside of their pH ‘Comfort Zone’.
Not only is this pH range of 6.5 – 8.5 ideal for Carp (Koi), except during spawning where a range of 6.5 - 8.0 is more suitable. It has also been proven that the range of 6.5 - 8.5 will promote the most diverse, healthy and productive aquatic life.
In our next post, we will begin discussing the Nitrogen cycle starting with Ammonia.
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