Hi and welcome to the forum
What are the tank dimensions (length x width x height)?
What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).
Depending on what the GH of your water is, will determine what fish you should keep.
Angelfish, discus, most tetras, most barbs, Bettas, gouramis, rasbora, Corydoras and small species of suckermouth catfish all occur in soft water (GH below 150ppm) and a pH below 7.0.
Livebearers (guppies, platies, swordtails, mollies), rainbowfish and goldfish occur in medium hard water with a GH around 200-250ppm and a pH above 7.0.
If you have very hard water (GH above 300ppm) then look at African Rift Lake cichlids, or use distilled or reverse osmosis water to reduce the GH and keep fishes from softer water.
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Cardinal tetras need a tank that is at least 30 inches long, preferably longer and most tetras (including cardinals) need to be kept in groups of at least 10 of their own kind.
Pygmy Corydoras are fine in tanks that are at least 18 inches long (preferably 2 foot long) and should also be kept in groups of at least 6 (preferably 10 or more).
Honey gouramis are fine in tanks that are at least 18 inches long and you could have 1 or a pr (pr being 1 male & 1 female). If you have 2 males in a small tank, they will probably fight, so unless you can sex the fish at the shop, just get one.
