[Kaikoura]

I just recently bought a dragon goby and two mollies. From the site of aqualandpetsplus.com, I learned that the goby tends to prefer brackish water, and the mollies can withstand saltier water. I've had them in the same tank for a few hours, and they don't appear to be bothering each other. Is it okay to keep them together indefinitely?

Edit: Can anyone tell me exactly what kind of salt is used for brackish tanks? (I know nothing like table salt)
Would aquarium salt work, or would I need to buy something else? I am going up to Petsmart tomorrow, so I hope to know sometime before we leave so I know what to get.
If anyone can help, that'd be amazing.