Nice fish that live in pairs?

Cardinals if they seem to be hanging out together already in the LFS tanks.
I wouldn't recommend mandarins unless the tank is at least a year old with a huge pod population.

 

3 lyretails, 3 chromis, 2clowns, 2firefish, bangaii cardinals, pajama cardinals, and other mated pair fish, do not get a pair of mandarin goby's though, in a 30g one would decimate the pod populus very fast and die but with two thats a disaster.

 

Certain dotties are hard to pair up and usually end up killing each other unless you put them in a special tank with a seperation.
But....
Orchid Dottybacks
Pseudochromis fridmani are an exception

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Orchid dottybacks are one of the most beautiful and peaceful members of the species. It's no wonder that they are the most popular dottyback in the marine aquarium hobby.


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Sexual Dimorphism

Pairing two juveniles will most likely form a male-female couple. When I started looking for a pair, I found a medium sized one and a smaller one. They paired up right away and were my first pair of fish to spawn.