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).
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Dwarf gouramis sold in most shops are normally all males and they are territorial to some degree. It is preferable to only have 1 male per tank.
Dwarf gouramis (Colisa lalius) and all their colour forms have a couple of health issues (gourami Iridovirus & Fish TB), neither of which can be treated.
If you want a small gourami, look for a different species (thick lip, Indian banded, sparkling, etc), they have fewer health issues.