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Pond Biology
You may not be able to control what’s in the water that you use for your pond but knowing a little water chemistry will help.
Carbon Dioxide
As the level of carbon dioxide is reduced, the pH level increases. Phytoplankton are microscopic aquatic plants that are responsible for most of the primary oxygen productivity in ponds and the “green water condition”. As phytoplankton use carbon dioxide, the pH of the pond water increases and during times when algae blooms occur, the pH may climb above 9 in ponds with low alkalinity (20 to 50mg/L). Well water often contains elevated levels of carbon dioxide, low pH, and low oxygen concentrations. Splash it or increase aeration as you fill your pond. Carbon dioxide in high concentration limits the capacity of fish blood to carry oxygen by lowering the blood pH at the gills.
pH
The concentration of bases and acids in pond water determines the pH. A low pH is considered acidic and a high pH is considered basic. pH often fluctuates one or more units during a 24 hour period. Prior to sunrise the pH level is often low due to carbon dioxide produced by green plant and fish respiration. Carbon dioxide forms a mild acid when dissolved in water. The highest pH readings generally occur when the dis¬solved oxygen levels are highest. The lowest pH readings often occur when the dissolved oxygen levels are the lowest (after sunset and before sunrise, on cloudy days and after cold rains). Most freshwater fish have an average blood pH of 7.4 and grow best in water with a pH range between 6.2-9.0.
Alkalinity
Is expressed as the buffering capacity of water in parts per million (ppm) of calcium carbonate. A suitable range for pond water is 20 to 300 ppm. Alkalinity can be increased by adding calcium carbonate, sodium bicarbonate, or calcium chloride. In ponds with moderate to high levels of alkalinity and hardness, the pH will be slightly basic and resist rapid changes but the more toxic form of ammonia (NH3) may increase. Ponds with alkalinities below 20 mg/L do not usually support green phytoplankton blooms. Metals like copper and zinc become more soluble in acidic water with low total alkalinity. Therefore by maintaining acceptable levels of alkalinity and hardness the toxic effect of these metals will be reduced.
Hardness
Is a measurement of positive ions (divalent salts) like calcium, magnesium and iron where as alkalinity is a measurement of negative ions (car¬bonate, bicarbonate). Fish utilized calcium and magnesium for bone formation, scale development, blood clotting and other metabolic reac¬tions. Hardness levels should be above 50 ppm. Low levels can be adjusted by the addition of lime or calcium chloride. Depending on the water source it is possible to have high alkalinity and low hardness or sometimes in the case of well water, high hardness and low alkalinity.
Carbon Dioxide
As the level of carbon dioxide is reduced, the pH level increases. Phytoplankton are microscopic aquatic plants that are responsible for most of the primary oxygen productivity in ponds and the “green water condition”. As phytoplankton use carbon dioxide, the pH of the pond water increases and during times when algae blooms occur, the pH may climb above 9 in ponds with low alkalinity (20 to 50mg/L). Well water often contains elevated levels of carbon dioxide, low pH, and low oxygen concentrations. Splash it or increase aeration as you fill your pond. Carbon dioxide in high concentration limits the capacity of fish blood to carry oxygen by lowering the blood pH at the gills.
pH
The concentration of bases and acids in pond water determines the pH. A low pH is considered acidic and a high pH is considered basic. pH often fluctuates one or more units during a 24 hour period. Prior to sunrise the pH level is often low due to carbon dioxide produced by green plant and fish respiration. Carbon dioxide forms a mild acid when dissolved in water. The highest pH readings generally occur when the dis¬solved oxygen levels are highest. The lowest pH readings often occur when the dissolved oxygen levels are the lowest (after sunset and before sunrise, on cloudy days and after cold rains). Most freshwater fish have an average blood pH of 7.4 and grow best in water with a pH range between 6.2-9.0.
Alkalinity
Is expressed as the buffering capacity of water in parts per million (ppm) of calcium carbonate. A suitable range for pond water is 20 to 300 ppm. Alkalinity can be increased by adding calcium carbonate, sodium bicarbonate, or calcium chloride. In ponds with moderate to high levels of alkalinity and hardness, the pH will be slightly basic and resist rapid changes but the more toxic form of ammonia (NH3) may increase. Ponds with alkalinities below 20 mg/L do not usually support green phytoplankton blooms. Metals like copper and zinc become more soluble in acidic water with low total alkalinity. Therefore by maintaining acceptable levels of alkalinity and hardness the toxic effect of these metals will be reduced.
Hardness
Is a measurement of positive ions (divalent salts) like calcium, magnesium and iron where as alkalinity is a measurement of negative ions (car¬bonate, bicarbonate). Fish utilized calcium and magnesium for bone formation, scale development, blood clotting and other metabolic reac¬tions. Hardness levels should be above 50 ppm. Low levels can be adjusted by the addition of lime or calcium chloride. Depending on the water source it is possible to have high alkalinity and low hardness or sometimes in the case of well water, high hardness and low alkalinity.