Freshwater Flounder

Question
I just obtained a Freshwater Flounder from a friend who couldn't keep it anymore, he had it in freshwater. But now that I'm reading up on it, it says it needs to be kept in a tank with about a 1/2 teaspoon of salt for every gallon.

I have a 20H Aquarium with the following:

7 Zebra Danios
1 Balloon Molly
1 4in Angel fish
1 2in Angel fish
1 Opaline Gourami
and the flounder...

If I add the salt will that hurt my other fish that currently live in the tank?
Also I am soon to have a salt water tank, can he eventually moved to all salt?  

Answer
Hi Kaori,
Freshwater flounders are so interesting. They do in fact prefer brackish water which is only genuine if it is made up with synthetic marine salt such as instant ocean marine salt. Regular aquarium salt is ok, but doesn't contain trace minerals to make true brackish water. The Flounder would probably be OK in water with some aquarium salt for a while, but would really thrive in true brackish water. Your other fish likely aren't going to tolerate too much more than the recommended amount of aquarium salt.

I haven't heard that they would tolerate as much salt as a fully marine tank.  It might be possible if the fish was gradually acclimated to it.

Here is a good article on flounders-
http://aqualandpetsplus.com/Oddball,%20Flounder.htm

I hope this helps!
Karen~