Both are fish I've kept for years, and I've visited the habitat of australe, though no fish were home at the moment to be caught. I don't have australe now, but had them for about 4 generations last time, and have kept them off and on for 30 years.
australe gold are an old aquarium colour mutation. They originate in Gabon. They are happiest and easiest to keep at 21-22c/70 to 72f. If you give them temperature stability, they will also do well warmer, as they come from a not very typical habitat with very still, seasonally warmer water. Some breeders will raise temperatures to get higher egg production, though it shortens lifespans. They're insectivores who like live, frozen and freeze dried foods more than flakes, though you may get away with bug bites flakes.
They are great jumpers. Heads up there - it's a serious problem with them. It's how they escape danger, and if they are spooked, up they go. Tight covers are essential.
gardneri or nigerianus, a Nigerian and northern Cameroonian species, can handle slightly warmer conditions as they tend not to live under the forest canopy. They breed and live best at 22 to 24, in my experience, up as high as 74 in fahrenheit. They can live shorter lives warmer, but it isn't ideal for them, or for you. Mine continue breeding in summer when the room gets above their range. I get lots of fry growing up with their parents. In winter, I have had tanks get down to 18c, and they did fine, still breeding slowly.
I use no heaters with my killies, which are all west and central African species like yours. Last summer when I fished in Gabon (and failed to catch australe) the average water temperature in the Aphyosemion habitats we caught fish in was around 22. The water was very soft, but wasn't tannin stained blackwater. The lower temperatures may seem odd around the equator in Africa, but the forest canopy has a cooling effect on the water.
You might want to go to the aka.org site, and under public library, have a look at the beginner's guide. There is an abridged version that's free, or at least there was.
