Rainbow fish are actually several different families of fish. What distinguishes each fish in this category is its shape and coloring. These fish have elongated bodies and fairly flat sides. Most have stunning colors, close to that of saltwater fish, and the males often develop a hump on their backs.
Rainbows are schooling fish, so if you want them to be as colorful and healthy as possible, keep them in groups of six or more of the same species. They are quite active and need plenty of room to swim, so do not over plant the tank. They need a roomy aquarium, as some of the species of rainbow can grow quite large.
Rainbow fish need medium to hard water with slightly alkaline pH levels. You must pay special attention to water quality when caring for rainbows, because the brilliant colors only display in good water. Put plants and other aquarium décor near the back of the tanks so the fish can have plenty of room to swim near the front.
Rainbow fish are often considered community fish. However, they can become quite aggressive, due mainly to their active personalities. Research the species of rainbow you intend to keep carefully before adding it to a community tank.
A high quality flake food can be a rainbow fish's basic diet. However, they need live or frozen foods for the best coloration. Brine shrimp, bloodworms, and white worms are all excellent foods for rainbows.