[Koi Kameon]

I bought a small 1/2" red claw crab. It's in brackish water at about 1.002 now since the store kept it in fresh. I have seen parameters for the water being anywhere from 1.002 to 1.005. What is best? Also, for the depth of the water, I've seen anywhere from 3 or 4 inches up to 8 inches. I was thinking about putting a few small fish in with it. Mollies being obvious, but I read somewhere that guppies could do minimal brackish water too. Anyone have any ideas? Thanks in advance since I can never figure out how to send out those thank you icons!

Addendum: more searching on the web and it looks like guppies actually like it a little brackish. Petco even recommends it. That is so different than twenty years ago when I last kept them...