Choosing and selecting the right fish that could live together in harmony in a community aquarium is sometimes a complicated process because there are many things to consider and it basically involves some basic research and work.
The instructable here is meant to share the idea and hopefully it help you to make the right decision. More information can also be found at http://allabout-aquariumfish.blogspot.com/
Step 1: Research and Info finding
The first step towards your research is to find out as much information as possible about the living condition suitable for the fish. There are different sources which you can refer to and all these are easily available from the internet or library.
Step 2: Grouping into same requirements
Fish basically can be grouped into saltwater or freshwater fish and it can be further divided into either those that live in tropical region or coldwater species. Saltwater fish need addition of salt with certain salinity to survive while freshwater fish is much easier to care for as no addition of salt is required.
Fish that belongs to tropical region generally will thrive in aquarium water ranging from 24 to 30 degrees Celsius while coldwater fish demand water temperature between 18 to 22 degrees Celsius. Therefore, in order to establish your community aquarium, you will need to select the fish that has the same requirements.
Step 3: Compatibility
Once you have done that, determine compatibility between each individual species. Certain fish are aggressive while others are peaceful. Therefore if you intend to get the right fish to mix together, make sure those aggressive types have their own tank isolated from the rest while grouping together all the peaceful community fish into the same aquarium.
Step 4: Determine full grown size
Another important consideration is to make sure that the fish tank is able to accommodate the size of full-grown fish species that you've selected. Don't be deceived by size because certain species if properly cared for can grow to very large. Your main aim is not to overcrowd the space that will lead to poor water quality.