The Great Salt Debate

[Minaku]

Over at the betta community at LiveJournal there was a discussion about types of salt and creating brackish water conditions. Every single pet store employee I have ever met has said to create brackish conditions using aquarium salt. Even the aquarium salt carton has directions on how to create brackish conditions. But isn't brackish water diluted seawater?

Now, I know a lot of brackish fish have been living in freshwater for so long that they're practically freshwater fish, but what's the logic behind telling someone they can duplicate an ocean-ish situation using plain ol' NaCl?

[amanichen]

minaku said:

Over at the betta community at LiveJournal there was a discussion about types of salt and creating brackish water conditions. Every single pet store employee I have ever met has said to create brackish conditions using aquarium salt. Even the aquarium salt carton has directions on how to create brackish conditions. But isn't brackish water diluted seawater?

Yes, yes it is. True brackish water is more than just NaCl in a solution...it's composed of many other trace elements and salts. The biggest difference is, that brackish water usually has a high pH, and simply adding NaCl to water doesn't give you a 7.6-8.0 pH with proper buffering to keep it in that range. Saltwater is also much harder than freshwater, with much more calcium and magnesium present (this is a critical thing for livebearers.)

but what's the logic behind telling someone they can duplicate an ocean-ish situation using plain ol' NaCl?

For the reasons I mentioned above, there isn't any logic. This goes along with people abusing a brackish water fish's ability to adapt to "full fresh" or "full salt," whereby people automatically think that the fish are instantly adaptable, and perpetually comfortable at either of the extremes.

[Minaku]

So when you're buying fish like mollies, it's best to buy sea salt to use in the tank, right?

Hmm. People always say bettas and livebearers, except guppies, can live together. I always thought they couldn't because of the fresh vs. brackish water divide, but so many people keep them together in fresh water. Would the livebearers have a decreased lifespan because of the fresh water, or does it not matter anymore because popular fish like those have been bred and lived in fresh water for so long?

[amanichen]

Forcing a brackish water fish to live in pure freshwater can be a dangerous practice when it is applied indiscriminately.

The "discrimination" part comes when you consider that some fish (livebearers and non-livebearers included) have been captive bred for generations, while others are still very close to wild, or directly from the wild. Certain livebearers would benefit from brackish conditions, but keeping them in freshwater won't necessarily kill them if they come from a long line of captive bred ancestors.

The simple answer to this is to find out where your fish came from (wild or captive) and then adjust things accordingly. This isn't always possible, but I'm sure if you were keeping a tank with only brackish livebearers then they'd appreciate the brackish chemistry.

[Minaku]

Thanks, Amanichen. I was already questioning whether or not freshwater and brackish water fish should ever be mixed; if I do get my platy tank as I plan, I'll definitely be making it brackish for them.