| As you can see, the use of salt in a koi pond system is a "religious" issue. But there are some unassailable facts about salt and koi... here are just a few:
1. salt, or more specifically chloride, is a physiological requirement of the fish to the extent that koi and goldfish are equipped with special cells in their gills called "chloride pumps" that do nothing but process chloride out of the water. Inside the fish, chloride is used to transfer waste out of the fish (simplistic view). Wanna do a nasty experiment?? Place a koi or cold in distilled water and see what happens to it. But don't walk away from it...
2. All natural freshwater has some level of chloride in it, ranging from .02 to .1% depending on where you live. City water tends to have lower amounts as this is "processed" water rather than natural.
3. The most beneficial use of salt is as a tonic for stressed fish. The increase in chloride in the water reduces the osmotic pressure gradient between the fish and the water and this allows the fish to "breathe" easier.
4. NEVER.... NEVER use salt above .1% in cold water. Increased salt levels in freshwater reduce the temperature at which freshwater reaches maximum density. From physics we know that freshwater reaches max density at 39.2 degrees. In a well designed system (depth-volume, etc.) this means that the water should get no colder than 39 degrees at depth. Increased chloride levels will reduce the max density temp and ultimately adversely affect our fish. There is a fine line between survival and death in cold water and we don't want to disrupt it with added chloride. Even a degree or two F can have an impact.
Just a couple of added points on salt...
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