I have kept several in tanks smaller then that, right now in my 24 gal nano I have a or of potters and a single fishers with no trouble. the main thing is lots of live rock for both foraging on algae and hiding places and to add them or introduce them in a way that they get used to each other. What I did to add the female potters, which I collected a year after the male was collected, was to put the female in a clear plastic container for a couple of weeks then I just removed the top and let her find her own way out, other then a little chasing every once in a while they get along great.