If you want to mix species, be sure to study up on what part of the clownfish family tree the specimens you would like are from. The ones who are more similar are more likely to get along, while those that swim with up/down movement tend to reject those who swim with side to side movement (and tomatoes tend to be too territorial to have patience enough to pair up successfully in smaller tanks). Be mindful of adequate escape routes for the weaker/smaller fish and introduce it to the part of the aquarium with most escape routes in it. Personally I keep a 60L nano with two polymnus and a macrodactyla. I introduced the youngest fish into the part of the tank that is heavy with escape routes and for a long time it preferred keeping its distance to the "big dangerous" older fish during the day time (they always slept in the anemone together). The older fish got annoyed over it but could never catch the smaller fish with all the escape routes. The dominant fish eventually stopped chasing and started developing a "lure" tactic instead. It took about a year before they fully paired up because the smaller fish would sometimes go and hang out in the part of the territory that it was first introduced in and the big fish spend a long time learning different lure tactics. Today they are dancing and playing around in their dedicated tank all day, everyday and it was wonderful seeing the social development of the bigger fish once it realised that chasing would not help it achieve what it wanted.
