07-27-2010, 09:33 PM
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I generally agree with you (Matt), but one has to be cautious here. Some inexperienced beginning aquarists might well get the impression salt is the best cure for ich or something else, when it is certainly not for some types of fish. Salt can severely stress and finally kill many soft water fish, and plants as well, especially at the high dose rates often suggested. I posted on this in two threads only last week, so here is what I said for the record: Salt makes the water more dense than the same water without salt. The aquarium contains water. The bodies of fish and plant leaves also contain water [just as we do--we are, what is it, 90-some percent water?]. The water in the aquarium and the water in the fish/plant is separated by a semi-permeable layer which is the cell. Water can pass through this cell. When either body of water is more dense, the other less-dense body of water will pass through the membrane to equalize the water on both sides. Water is constantly passing through the cells of fish by osmosis in an attempt to equate the water inside the fish (which is more dense) with the water in the aquarium. Put another way, the aquarium water is diluting the fish's body water until they are equal. Freshwater fish regularly excrete this water through respiration and urination. This is the issue behind pH differences as well as salt and other substances. It increases the fish's work--the kidney is used in the case of salt--which also increases the fish's stress in order to maintain their internal stability. Also, the fish tends to produce more mucus especially in the gills; the reason now seems to be due to the irritant property of salt--the fish is trying to get away from it. There is varying opinion on salt, I admit that; but I have never yet found one written authority who recommends salt in a freshwater aquarium in general, only as a medication/treatment for something. Dr. Stanley Weitzman, Emeritus Research Scientist at the Smithsonian and an acknowledged authority on characoid fishes (tetras, etc) writes that 100 ppm of salt is the maximum tolerated by characins, and several species show considerable stress leading to death at less, 60 ppm. 100 ppm is equivalent to .38 of one gram of salt per gallon, which is about 1/15 of one teaspoon [one level teaspoon is 6 grams]. This is why I do not recommend salt, whatever it may say elsewhere.