Kribensis are adaptable to a wide range of conditions. You can keep them in soft or hard water. Actually, I think pH will alter the ratio of males and females in a spawn. They may not be the best litmus test for South American apistos.
IMO, a lot of South American cichlids do fine as long as you keep their water really clean and you feed them well. There are exceptions to that, but overall I do not alter my water and I've had great luck with all sorts of SA fish. Spawning may or may not happen if the fish don't like your parameters, but that's something you could adjust later if you wanted to try your hand at that. Why not set up a smaller tank and start with a trio just to see how they fare?
IMO, a lot of South American cichlids do fine as long as you keep their water really clean and you feed them well. There are exceptions to that, but overall I do not alter my water and I've had great luck with all sorts of SA fish. Spawning may or may not happen if the fish don't like your parameters, but that's something you could adjust later if you wanted to try your hand at that. Why not set up a smaller tank and start with a trio just to see how they fare?