You have probably been to your local pet shop or aquarist dealer and seen a large variety of tropical fish to choose from. How do you go about choosing the right combination of fish for you?
You can't just choose any fish you like and expect them to all get along well together, it doesn't work like that - you need a plan.
Firstly, do you want a community aquarium or a species tank? A community aquarium will hold a variety of different fish that will all live in harmony with each other. A species tank, as the name suggests, will only hold one variety of fish.
Most people start with a community aquarium, and it is a very good place to start.
Before you work out exactly which fish you want, you need to work out have many inches (or centimeters) of fish you can accommodate in your new aquarium. A long, shallow tank will hold more fish than a short deep tank, because it is the amount of oxygen in the water that is more important than the actual quantity of water.
As a guide you can expect to be able to fit one inch of fish for each gallon of water, so a good place to start is to calculate the number of inches of fishes you can accommodate. This is measured from the mouth of the fish to the start of the tail, and don't forget to find out how big the fish will grow to, don't just look at the size of them in the shop as they will almost certainly grow.
How do you go about choosing the right fish for you? Firstly look around and see if there are any fish which you definitely want, and start your plan there. You need to know what size the fish you want will grow to, and how many you should keep together. Some fish are fine singly or in pairs, others only really thrive when they have friends to shoal with.
When you have chosen the fish you want to base your aquarium on, look to see how many you need to get, and how many inches they will use up. Next, will they live in harmony with all other fishes, or are there some they don't get along with? Also, take note of where they live in the aquarium. Some fish are bottom dwellers, some live mainly at the top, and others in the middle of the aquarium.
The best way to have a balanced aquarium is to have some fish that live in each level of the aquarium, as well as some fish that will keep the bottom clean, like corydoras. I also always like to have fish that will keep the sides clean, like a pleco (suckermouth catfish).