i was wondering do gobies mix well with each other and does the size of the tank matter . . . I currently have a 6ft 90g and have one golden headed sleeper gobie ( Valenciennea strigata ) and my fiance wants to introduce a pair of purple firefish goby ( Nemateleotris magnifica ). I dont know much about the species but the one i have is about 4 inches while the new pair of firefish would be much smaller at about 2 - 3 inches . . . Will i have trouble in paradise???