Marine Salt Vs. Aquarium Salt

wolfdog01

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Just want to start by saying I do not need to treat any fish, my betta is healthy and my snails are active, this is just a question of curiosity.
Say you needed to treat a freshwater fish for an illness and you had to use salt. What if you only had marine salt on hand, is there a difference between that salt and aquarium salt? Or really any salt used for fish. Is it the quantity or is there something in marine salt that is harmful to freshwater?
Also, kind of a dumb question, do marine fish ever have to be treated with small doses of freshwater?
I don't plan on having a saltwater tank but I just started thinking about these things lol.
 

DutchAquarium

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Aquarium salt is just NaCl while your marine salt is going to contain all the other minerals such as MgS04. I wouldn't add marine salt to a freshwater aquarium because first, it's more expensive, and you don't know how the MgS04 is going to affect the water in the freshwater. I also highly recommend not adding salt to freshwater aquariums ever, since this is actually more harmful to your inhabitants in most cases. This was a myth that started 50 years ago and still practiced.
 

Lorekeeper

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+1 to DutchAquarium.

I don't add any sort of salt to my FW tanks, and while it may have some therapuetic qualities (I'm not sure if that's just a myth or not), I've never found it to replace a good WC, or help in anyway.

As for marine fish, you can get rid of certain parasites (such as ich) with freshwater baths. Catch the fish, place it in a small container of freshwater for a few minutes, and put it back in the tank. Usually, the fish will handle the freshwater well for a few minutes, while the parasite immediately starts to suffer. There are also hyposalinity treatments, which is a commonly used way to cure ich. Pretty much, lower the salt level in the water to low-brackish, and ich will slowly begin to die off, while the fish can live in that water for a few months.

As for the quantity issue, the reason you can't add a freshwater fish to a saltwater tank is due to how they deal with salt regulation. A freshwater fish will be constantly trying to retain salt in it's body, so when you place it in a saline environment, the fish gathers salt to the point of dehydration. With a saltwater fish in freshwater, it's the exact opposite. A saltwater fish will constantly be trying to get salt out of it's body, so when placed into a freshwater environment, it basically drowns.

That said, there are some fish that can tolerate freshwater, brackish, and saltwater. These are known as euryhaline fish. The most common that people will usually know is the molly (I just added one to my reef tank today, actually), and guppies will usually have a pretty high salt tolerance as well. Fun fact!
 
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wolfdog01

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Wow! Lots of info guys! Thanks, I really liked reading the posts. Learn something new everyday.
I always heard salt in freshwater was used to help build a slim coat through irritation. Mind you, I can't remember the last time I used salt, because my old betta had fin rot and salt made it worse, water changes made it better. Since then I've only use salt dips to get pest snails off of plants.
 
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