I've never kept african cichlids before but I've been looking at some stock lists and the Altolamprologus Calvus look incredible! I really love the yellow, black and black congo white pearl ones. What are their water requirements? What is their temperament like? Can you keep multiple colored calvus together without the risk of crossbreeding? What tankmates do well with them? How many can be safely kept in a 75 gallon tank? I may have an empty 75 in a few months and am thinking of getting some calvus for it. Thank you in advance for your help!