hi, i've been gathering info for myself and turning it into a book for quick reference. epsom salts are used as a laxitive for bloated fish, it helps them pass food, usually used in combination with fasting. Aquarium salt is general use and can be added to any aquarium at a rate of 1 tbsp/gal, according to this an other sites. Go to diseases and prevention part of the forum and read the stickies. Very informative. Interestingly enough i stumbled across some info that give a strong case not to use salts at all, unless absolutly needed. Here it is:
Salt is detrimental to freshwater fish and plants in varying degrees. To understand why, we must understand what salt does in water.
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.
But as you asked specifically about plants: when salt is added to the aquarium water, the water inside the plant cells is less dense so it escapes through the cells. The result is that the plant literally dries out, and will wilt. I've so far been unable to find a measurement of how much salt will be detrimental to plants; all authorities I have found do note that some species are more sensitive than others, and all recommend no salt in planted aquaria.
I have an interesting measurement for fish. Dr. Stanley Weitzman, who is Emeritus Research Scientist at the Department of Ichthyology of the Smithsonian Institute in Washington and an acknowledged authority on characoid fishes, writes that 100 ppm of salt is the maximum for characins, and there are several species that show considerable stress leading to death at 60 ppm. 100 ppm is equal to .38 of one gram of salt per gallon of water. One level teaspoon holds six grams of salt. You mention 1 to 3 teaspoons per gallon. If you have characins in this tank, that would be 6 to 18 grams per gallon, which is at minimum 15 times the amount they tolerate. Livebearers have a higher tolerance (mollies exist in brackish water) so the salt may be safe for them.
Now perhaps you know why I never recommend salt.
Read more: http://www.tropicalfishkeeping.com/a...#ixzz1vAo7eVBb
Thought this was an interesting read, possibly worth adding to stickies?