Effects of High and Low pH Levels in Water on Fish

Effects of pH Levels on Aquatic organisms
Very high ( greater than 9.5) or very low (less than 4.5) pH values are unsuitable for most aquatic organisms. Young fish and immature stages of aquatic insects are extremely sensitive to pH levels below 5 and may die at these low pH values. High pH levels (9-14) can harm fish by denaturing cellular membranes.

Changes in pH can also affect aquatic life indirectly by altering other aspects of water chemistry. Low pH levels accelerate the release of metals from rocks or sediments in the stream. These metals can affect a fish’s metabolism and the fish’s ability to take water in through the gills, and can kill fish fry.

The term "pH" was originally derived from the French term "pouvoir hydrogène," in English, this means "hydrogen power." The term pH is always written with a lower case p and an upper case H. (Colorado.us)

Student at BCC Aquaculture Center, testing pH levels in water.

High pH Levels Effect
At high pH (>9) most ammonium in water is converted to toxic ammonia (NH3), which can kill fish. Moreover, cyanobacterial toxins can also significantly influence fish populations. (lepo.it.da.ut.ee)

High pH level.


Water sample which indicate a high pH level when test, in this case could be adjusted by straining water through peat. The instructor at BCC compared it to "tea," which is dark, but safe for fish. Added to the aquarium, the pH level was brought down within a safe range.


All images, including Aquaculture Facility located here.

Fish kill at low pH in a Norwegian river
Zoological Laboratory, University of Bergen, 5000 Bergen, Norway.
THE decline in freshwater fish populations in parts of southern Norway is associated with increasing acidity in rivers and lakes1. The salmon has been eliminated from many rivers, and hundreds of lakes have lost their trout populations. The chief cause of increased acidity is acid precipitation which is the product of the emission, oxidation and long-distance transport of air pollutants, particularly sulphur dioxide2,3. Similar observations of acid rain and the disappearance of freshwater fish populations have been made in the United States, Canada and Sweden4−6. (Nature.com)

The Acid Test: Is Your Pond pH Too Low?
News from Texas A&M University, 3/24/2006, R. Burns
Winter months are an ideal time to adjust pH and alkalinity because the treatment, usually an application of agricultural lime, takes time to have an effect," Higginbotham said. "Depending upon weather conditions, the fineness of lime used and the method of application, the time delay may be from a few days to as much as a month."
Alkalinity relates to the "buffering capacity" of water, its capacity to reduce fluctuations in pH, he said.
Pond water pH becomes low – acidic – primarily because local soils are acidic. But not all soils are acidic; not all ponds need liming. The best way to know for certain is to have a simple water test done to determine both alkalinity and pH, Higginbotham said.
But generally, acid soils and consequently acid pond water are problems confined to East Texas.
"The further east of I-35 you go, and the further north of I-10, the higher the likelihood you need to lime your pond," he said. "Another way to determine if you might need to lime is if there's an agricultural liming service in your area. If not, then you probably don't need to lime your pond."
Water pH and alkalinity must be correct for pond fertility programs to work. In such a program, fertilizers containing nitrogen, phosphorus and potassium are added to encourage the growth of microscopic plants called phytoplankton. Microscopic animals called zooplankton feed on the phytoplankton, Higginbotham said.
And many forage fish, including bluegill, feed on the zooplankton. Game fish, such as largemouth bass, feed on the bluegill. The result of a properly managed fertility program is better fishing, and since the phytoplankton absorb wastes, better recreational use of the pond overall. Proper liming can improve phosphorus availability and enhance the health of the pond.
But even without a fertility program, liming can make the critical difference to fish health, particularly where soils are highly acidic such as East Texas, Higginbotham said. Low pH values are usually coupled with low alkalinity.
"Total alkalinity below 20 parts per million can result in large swings in daily pH values, which can stress fish," he said. "And a pH below 5.0 approaches the 'acid death point' for many fish species." (Continued... USDA)

Fish kills resulting from low pH (acidic water) are even less common than chemical kills. Usually pH kills occur when heavy rains wash tannin (an acidic substance found in leaves) from wooded areas. Low pH can be increased easily by applying agricultural limestone. The amount of lime required can be determined by sending samples of the mud from the pond bottom to the NCDA Soil Analysis Laboratory for analysis. (See the earlier section on liming procedures.) Contact your county Agricultural Extension Service office for assistance in sending soil samples. (NCSU)

[(+/-) 1500 pixels 106 k] The pH of some aqueous solutions: Measurements of pH are usually made with a meter connected to a glass electrode immersed in the solution.

Low ph in Oceans (related to climate change from emmissions) and Carbonic Acid
Acid seas threaten to make British shellfish extinct
Sunday 12 March 2006, From Plymouth Marine Laboratory
SHELLFISH, crabs, lobsters and a host of other familiar species could become extinct around Britain and Europe because our seas are becoming steadily more acidic.
An official report is to warn that carbon dioxide generated by human activity, already linked to climate change, is also sharply altering the chemistry of the oceans. The gas forms carbonic acid when it dissolves into sea water.
Some species, such as corals and certain plankton, are so sensitive to the rising acidity that they could be in rapid decline within decades. Others, such as crabs, mussels and lobsters, are more resistant, but they too will be in danger by the end of the century. All the affected organisms build their shells or skeletons from calcium carbonate, a mineral they extract from sea water but which is attacked by carbonic acid.
(pml.ac.uk - Shellfish) and Ammonia, an alkali, would increase the pH whereas the oceans are becoming slowly more acidic (lower pH) because the additional CO2 we are dumping into the atmosphere is dissolving in the water giving carbonic acid: (Carbonic Acid)

Temperature and affect on Gas / Water
Why carbon dioxide is more soluble (the ability to dissolve in water) in cold water than it is in warm water.
All gases are more soluble in cold water than in warmer water. This is a general trend. The reason has to do with the thermodynamics of the reaction: GAS(in solution) = GAS(gas phase) The entropy change, delta S, of this reaction is always positive because the gas molecules are less constrained than the gas molecules in solution. The change in Free energy of reaction with an increase in temperature is the negative of delta S. The bottom line is that the solubility of gases decreases with increasing temperature. This effect is particularly large for gases like CO2 that undergo specific reactions with water. Ammonia would be another example.
The principle gives us the fact that a dissolved gas (carbon dioxide in this case) always becomes less soluble with increasing temperature. One can testify to this from experience that much more gas is released from a can of soda that is opened when it is warm rather than when it is cold. This illustrates that temperature effects the solubility of a gas. (Carbon Dioxide and Solubility)