If you want to pair up and don t want to use a partition in a well-built tank, first put two fish in each tank.

If you want to pair up and don’t want to use partition board in a well-built tank, you should first raise two fish in their respective tanks to be fearless of others, then take one out of the other tank and separate them with isolation box.
Wait until it’s not exaggerated. Every day, it’s okay to let the two fish interact. The gentle tea like milk tea can match up quickly.