Hi. I am interested in putting together a Central American livebearer biotope tank with sailfin mollies or alternatively Poecilia sphenops, swordtails, and maybe porthole livebearers. I may add in a freshwater goby or two. I am hoping someone can tell me how many of each of these livebearers I can fit in a 75 gallon tank without overstocking and overcrowding and how much salt I need to add if any. My water is very hard and has a pH of around 8 or so. Any suggestions on alternative livebearers or other compatible tank inhabitants would be welcome also. I was interested in Goodeids but I cannot find a lot of information on them. Thanks in advance.

Karen