Can freshwater bacteria live in saltwater?

[swhastan]

I heard the story that a person who is running both saltwater tank beside freshwater tank provides top-off water from freshwater tank to saltwater tank. According to him, it's much better because matured water can be supplied.
As far as I know, the bacteria in both water are different and cannot live in the other place.

What's the truth?

[sevise]

I wouldn't topoff from a FW tank because it would add nutrients, nitrates to the tank. Evaporation is more or less pure H2O, topping off with RODI means your replacing that water with pure H2O.

[duec22]

You know I don't think I would be doing that. First off no fresh water bacteria can not live in salt water. Second I would think that the water in the FW tank isn't the cleanest source of top off water. I have no idea what "mature" water is...maybe he's useing tap water and he's talking about the clorination levels.

[ferventforager]

If by mature he means higher in nitrates then he may be correct, but I would not want to raise my nitrates. Freshwater bacteria cannot live in saltwater for the same reasons that fish cannot. Living organisma in water must maintain an osmotic balance. That is that saltwater fish have to rid themselves of salts to maintain the correct salt levels in their blood, but freshwater organism have to rid their body of water to maintain the balance. If you put a FW fish in salt it will die becuase the salt levels in its body get too high and when SW fish go into FW the salts levels get too low. It is some basic cell biology.