Adding Salt To A Freshwater Tank?

Question

I've read that adding salt to a freshwater tank will help fight some fish diseases. What exactly does salt do, how much would you add, and which diseases does it fight? I am not planning on adding salt to my tank, but I would like to know in case it's needed for future reference. Thanks!

Answer 1

I'll try to explain this is some basic terms. What the salt does is change the osmotic pressure within an organism. If you think back to your school science classes, maybe you'll remember the idea of diffusion - that molecules want to be spread out evenly. This is true, even when there's a membrane (cell membrane in this case) in between. Water can move freely to either side, but salt cannot. So for the concentration of salt in the water to be the same on both sides of the membrane, it's the water that has to move.

In freshwater, there's not a lot of salt in the water. All organisms need some salt to be healthy (it's used to produce stomach acids, to conduct nerve impulses, and to move other minerals in and out of cells). Fish have specialized cells on their gills specifically from removing small amounts of salt from the water, and they're capable of storing this inside of their cells. Parasites and fungi (what salt is generally used to treat) don't have the same mechanisms. So when they encounter salt, the water is pulled out of their cells to try and make the salt content inside and out balance. What literally happens is that these organisms dehydrate in a tank full of water because the salt pulls the water out of their cells.

In saltwater, you can do the same for parasites by lowering the salt concentration so they fill with water and burst.

Another benefit of salt in a new tank is that it eases stress from nitrite exposure by binding to the sites where nitrite is absorbed - nitrite interferes wih the uptake of oxygen, so when nitrites are high, fish will be at the surface looking like they're gasping for air.

For most fish, a tablespoon per 5 gallons is enough. Some species (especially livebearers) can tolerate much higher levels, while others (tetras, scaleless fish, catfish) are more sensitive, but all can tolerate the amount listed above.

For more info about using salt (and I tried to find some non-technical reading), see the links below:

Answer 2

do NOT add iodized salt.. the iodine is bad.. gotta use cheapo uniodized salt if you do it.. there seems to be a 50 50 split on this but the premis is that small quantities of salt occur naturally in fresh water from runoff, rocks, etc. this in turn helps the coating on a fish body to protect it from illness. i have had 50 gallon tank for 2 years. i tried with & without & found no difference in fish health. i have read that the benefit is so small that people should consider more helpful things like the additives found in typical pet shops. when i did add salt, it was 1-2 tablespoons for 50 gallon tank. like i said, no diff with or without..