i have two i keep by each other with no problems but my 3rd i have to keepo seperate. It does not play nice!!!
Their is no way to tell beside put them next to each other and watch them. First sign of one getting stung by the other then seperate them. Good luck. They are beautys, but must be placed with caution. My one frag, 1" big or so has long 3" sweapers!!!