Congratulations on your new aquarium! A 20 gallon tank is a great size for a variety of fish and aquatic plants. When considering what fish to add to your tank, it's important to keep in mind the size and temperament of the fish, as well as their compatibility with each other.
One fish species that would do well in a 20 gallon tank is the neon tetra. These small, colorful fish are easy to care for and enjoy swimming in schools. Another option is the dwarf gourami, which is a peaceful fish that adds a lot of color to the tank.
If you want a fish that is a bit more active, you could consider adding a school of harlequin rasboras. These fish are energetic and enjoy swimming in groups. Another option is the platy, which is a hardy and colorful fish that is great for beginners.
When choosing fish for your tank, it's important to avoid overstocking. As a general rule of thumb, you should have no more than one inch of fish per gallon of water. This will ensure that your fish have plenty of room to swim and thrive.
In addition to fish, you may also want to consider adding some live plants to your tank. Plants not only add visual interest to the tank, but they also help to maintain water quality and provide a natural habitat for your fish.
Overall, there are many fish species that would do well in a 20 gallon tank. By doing your research and carefully selecting your fish, you can create a beautiful and healthy aquatic environment for your new pets.