02-04-2012, 01:08 PM
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Originally Posted by yyankeeyankeefan
i use aquarium salt in my daughter's tank. i tablespoon for a 10 gallon. is that a bad idea? i have always had it in there. is it good for prevention (what i was told at the pet store)? or should i stop using it and just let it dilute out?
It depends upon the fish species but generally speaking salt does not belong in a freshwater aquarium. The idea that it can "prevent" health problems is a myth, and as the linked article shows it may even encourage some parasites so in these situations it has the opposite of the intended effect.
I am not a believer in using salt in any freshwater tanks. As that article also noted, it "works" (when it works) partly by causing the fish to secrete more mucus, especially in the gills, because the poor fish is trying to get away from the irritation of salt. If you happen to cut your finger, dip it in salt and you'll see why, or if you get it in your eyes; salt is a strong irritant.
There is scientific evidence that some fish species, those from soft water, have real physiological problems with salt in the water and at quite low levels. I've written on this previously, so I'm just going to paste my earlier ramblings here to add the explanation. A two-part article in TFH (June and July 1996) authored by Stanley Weitzman, Lisa Palmer, Naercio Menezes and John Burns, dealt with “Maintaining Tropical and Subtropical Forest-Adapted Fishes.” In this, the authors mention that 100ppm of salt is the maximum that can be tolerated by characins, and several species show considerable stress leading to death at a level of 60ppm. To put this in perspective, 100ppm is approximately equal to 0.38 gram of salt per gallon of water. One level teaspoon holds six grams of salt, so 1 teaspoon of salt in 16 gallons of water will cause stress, and in some species imminent death. Livebearers have a higher tolerance (mollies sometimes temporarily exist in brackish water) so the salt may be safe for them, but it may still pose a possible risk long-term for most of them. 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, 70-some percent water?]. The water in the aquarium and the water in the fish/plant are 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 is due to the irritant property of salt--the fish is trying to get away from it.