Suspended solids make the water cloudy or opaque; they include chemical precipitates, flocculated organic matter, living and dead planktonic organisms, etc.
"Solids" in water leave tangible residues when the water is filtered (suspended solids) or evaporated to dryness (dissolved solids). Suspended solids make the water cloudy or opaque; they include chemical precipitates, flocculated organic matter, living and dead planktonic organisms, and sediment stirred up from the bottom on a pond, stream, or raceway. Dissolved solids may color the water but remain clear and transparent; they include anything in proper solution.
"Turbidity" is the term associated with the presence of suspended solids. Analytically, turbidity refers to the penetration of light through water (the lesser the penetration, the greater the turbidity). Still, the word is used less formally to imply concentration (weight of solids per weight of water).
Turbidity over 100,000 parts per million does not affect fish directly, and most natural waters have far lower concentrations than this. However, abundant suspended particles can make it more difficult for fish to find food or avoid predation. To the extent they settle out, such solids can smother fish eggs and the bottom organisms that fish may need for food. Turbid waters can clog hatchery pumps, filters, and pipelines.
In general, turbidity less than 2,000 parts per million is acceptable for fish culture.
Acidity refers to the ability of dissolved chemicals to "donate" hydrogen ions (H+). The standard measure of acidity is pH, the negative logarithm of hydrogen-ion activity. The pH scale ranges from 1 to 14; the lower the number, the greater the acidity. A pH value of 7 is neutral; that is, there are as many donors of hydrogen ions as acceptors in solution.
Ninety percent of natural waters have pH values in the range 6.7- 8.2, and fish should not be cultured outside the range of 6.5- 9.0. Many fish can live in waters of more extreme pH, even for extended periods, but at the cost of reduced growth and reproduction. Fish have less tolerance of pH extremes at higher temperatures. Ammonia toxicity becomes an important consideration at high pH.
Even within the relatively narrow range of pH 6.5-9.0, fish species vary in their optimum pH for growth. Generally, those species that live naturally in cold or cool waters of low primary productivity (low algal photosynthesis) do better at pH 6.5- 9. Trout are an example; excessive mortality can occur at pH above 9.0.
The affected fish rapidly spin near the surface of the water and attempt to leave the water. Whitening of the eyes and complete blindness also occur, as well as fraying of the fins and gills with the frayed portions turning white. Death usually follows in a few hours. Fish of warmer climates, where intense summer photosynthesis can raise pH to nearly 10 each day, do better at pH 7.5- 9. Striped bass and catfish are typical of this group.
Alkalinity and hardness imply similar things about water quality, but they represent different types of measurements.
Alkalinity refers to an ability to accept hydrogen ions (or to neutralize acid) and is a direct counterpart of acidity. The anion (negatively charged) bases involved are mainly carbonate (CO:;) and bicarbonate (H C O 3) ions; alkalinity refers to these alone (or these plus O H- ) and is expressed in terms of equivalent concentrations of calcium carbonate (C a C 0 3).,
Hardness represents the concentration of calcium (C a++) and magnesium (M g++) cations, also expressed as the CaC0 3- equivalent concentration. The same carbonate rocks that ultimately are responsible for most of the alkalinity in water are the main sources of calcium and magnesium as well, so values of alkalinity and hardness often are quite similar when all are expressed as CaC0 3 equivalents.
Fish grow well over a wide range of alkalinity and hardness, but values of 120- 400 parts per million are optimum. At very low alkalinity, water loses its ability to buffer against changes in acidity, and pH may fluctuate quickly and widely to the detriment of fish. Fish are also more sensitive to some toxic pollutants at low alkalinity.
Various substances toxic to fish occur widely in water supplies as a result of industrial and agricultural pollution. Chief among these are heavy metals and pesticides.
Heavy Metals: There is a wide range of reported values for the toxicity of heavy metals to fish. Concentrations that will kill 50% of various species of fish in 96 hours range from 90 to 40,900 parts per billion (ppb) for zinc, 46 to 10,000 ppb for copper, and 470 to 9,000 ppb for cadmium. Generally, trout and salmon are more susceptible to heavy metals than most other fishes; minute amounts of zinc leached from galvanized hatchery pipe can cause heavy losses among trout fry, for example. Heavy metals such as copper, lead, zinc, cadmium and mercury should be avoided in fish hatchery water supplies, as should galvanized steel, copper, and brass fittings in water pipe, especially in hatcheries served by poorly buffered water.
Ultra Violet (UV) filters