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Water Chemistry


As hardy as our fish are, long exposure to poor water quality will cause stress and disease. Unfortunately, we cannot rely on our unaided senses to determine water quality — clear water is not an indication of good water quality from our fish’s perspective. Poor quality stresses our fish, which in turn causes their immunize system to go down, which in turn makes our fish susceptible to disease. In order to know if there is good water quality, it only makes sense to test it periodically rather than wait for disease systems to appear.
    Fish waste and other organic debris are the first steps of the nitrogen cycle, a series of events that produces some of the compounds we test for — ammonia, nitrites, and nitrates. Normally, we should test for PH, ammonia, nitrites, and nitrates every week or two. Testing should be made more frequently during periods of change in our ponds, such as spring warming, new filter installation, major pond cleaning or repair.



PH indicates the ratio of hydrogen ions to hydroxyl ions on a logarithmic scale from 0 (pure acid) to 14 (pure alkaline). Fish do best in water with a PH of 7.0 to 8.5. They can actually tolerate a wide range, but cannot tolerate a rapid change. PH affects the free ammonia/ionized ratio, with a higher PH resulting in a greater concentration of free ammonia. To make things more complicated, algae and other water plants can drastically change a pond’s PH from night to day, due to a change in the amount of dissolved carbon dioxide present in the water. We’re concerned about rapid PH shifts not only because of the ammonia ratio, but also because the fish are trying to keep their blood PH level during these shifts, thereby causing stress. PH needs to be adjusted slowly.



Ammonia introduced by fish waste and decomposing organic debris, is the most toxic nitrogen compound. It is present in two forms. Free and ionized. Free ammonia is the most toxic and will cause death in very low concentrations. Problems associated with non-lethal elevated levels of ammonia include gill disease, dropsy and fainter. The higher the PH and the temperature, and the lower the salinity or hardness, the more toxic the ammonia. With a properly functioning biological filter, the ammonia is usually zero.


Nitrite is less toxic than ammonia, but still very toxic as it inhibits the ability of the blood to carry oxygen. Nitrite is oxidized into nitrate by nitrobacteria bacteria living in the filter.


Nitrate is the end product of the nitrifying phase of the nitrogen cycle. It is much less toxic than either ammonia or nitrite. It is how ever, a nitrogen compound that is the food and fertilizer for algae. In nature, nitrate is absorbed by water plants and is reduced into free nitrogen by anaerobic bacteria living in the bottom silt. Hydrogen sulfide and methane gas are given off as a by-product of the anaerobic filtration. An oxygenated, clean pond will not have any anaerobic bacteria present, so nitrates will accumulate in the pond. Partial water changes of 1/10th per week will flush out the accumulating nitrate.


Dissolved Oxygen is usually only a warm weather concern, as it is associated with water temperature and algae. However, the larger the fish, the greater the oxygen demand. Low levels of oxygen allows you to determine if your pond has the maximum amount of oxygen for the temperature of the water.


Salt Level Test -- pond fish actively maintain a natural balance of electrolytes in their body fluids. Electrolytes such as potassium, sodium, chloride, calcium, and magnesium are removed from the water by chloride cells located in the gills. These electrolytes are essential for the uptake of oxygen and release of carbon dioxide and ammonium across gill membranes. The lack of electrolytes can cause serious health problems to the fish. During periods of disease and stress, healthy gill function is disturbed. This can lead to the loss of electrolytes through the gills, sometimes call osmotic shock. Osmotic shock interrupts healthy gill function by reducing the intake of oxygen and the release of carbon dioxide and ammonium from the fish. Rock salt overfeeding can lead to elevated nitrite levels especially in newly set up ponds. The nitrite ion NO2 enters the gills and prevents the blood from carrying oxygen resulting in nitrite toxicity. Rock salt will temporarily block the toxic effects of nitrite while corrective action is taken.


A Pond Thermometer is important to check pond’s water temperature to maintain fish on correct feeding schedule. Testing gives you the information you need to ensure the best possible conditions for your fish, as well as the information to maintain water clarity.