Nope to have a actual brackish tank you have to have partial salt water like in the ocean. So you need to use something like instant ocean. They have other things in them becides just salts. Like calcium, minerals,etc,etc. And freshwater salt is just pure salt. So any pure salt will work for that. Like rock salt, water softner salt(as long as its the pure kind)(morton brand blue bag), kosher salt.
never heard of it (weird huh), so i wouldnt know; but id say no . just get some sea salt (not the one for food) i mean its like $20 for a bag and you dont use that much.