The parameters of your source water, presumably tap water, is what you/we need to know before selecting any fish. Don't waste money on tests for this, but see if the data is posted on the website of your municipal water authority (assuming you are on city water and not a private well). GH (general hardness) is the most important, and once you know what this is for the tap water, it is not going to alter much in an aquarium. Knowing the KH (carbonate hardness, also called Alkalinity) is helpful, as this buffers pH. And then, the pH. And you should have a pH test before getting fish as this is one water test you can do regularly or periodically and it can alert you to issues as it is influenced by what goes on biologically within the aquarium. It is essential in any aquarium that the pH be as stable as possible, because of the impact it has on fish.
