In ancient China, goldfish could only belong to royal members of the Song Dynasty but today, goldfish have become popular as pets, especially in the United Kingdom where they are in third place, only to dogs and cats. Silver dollar fish are hardy and relatively easy to keep. Both are long-lived and both add splashes of color to any freshwater aquarium. Goldfish and silver dollar fish survive in very different habitat needs, though, making them unsuitable to house together.
The Dominant Cold-Water Fish
Goldfish have a good tolerance for fluctuations in water temperature, but typically don't like water above 75 degrees Fahrenheit. Water shouldn't be allowed to get too cold either. Fancy goldfish fail to thrive in water below 60 degrees Fahrenheit, and goldfish stop eating when water temperatures fall below 55 degrees. In addition to requiring cooler water than tropical fish, goldfish can grow quite large and require a lot of room to move about. They eat a lot, including any smaller fish they might share a tank with. The abundance of waste produced by goldfish can create an ammonia-filled environment and place a lot of stress on your filtration system, not to mention the stress it can cause to more environmentally sensitive tropical fish.
Goldfish are best kept with other goldfish, and even then, common or comet goldfish shouldn't share a tank with fancy goldfish. The slower, sight-impaired fancy goldfish will struggle for food and will likely end up with nibbled fins. If you desire variety in your aquarium, try white cloud minnows or zebra danois. Both are schooling fish, so add at least three but preferably four to six, and ensure they're large enough that your goldfish can't snack on them.
Fish You Can Bank On
Silver dollar fish, native to rivers in South America, need a warm aquarium in order to survive. While the goldfish does not like water above 75 degrees Fahrenheit, the silver dollar only begins to get comfortable at that temperature, and prefers water between 78 to 84 degrees Fahrenheit. Silver dollars will only breed in the higher temperature ranges. Silver dollars have the potential to grow to a size of 6 inches, making them a fairly large freshwater fish. Highly social schooling fish, silver dollars are happiest when you house four to six of them together. Primarily herbivores, silver dollars are known to feed voraciously on any live plants kept in the aquarium.
Fair Weather Friends
Silver dollars are generally peaceful and can live in happy harmony with nearly any variety of tropical freshwater fish. If housed with aggressive fish, such as the African cichlid, silver dollars can become aggressive as well. Before increasing the number of fish in your tank, ensure it will be large enough to accommodate full-grown silver dollars with ample room left over for your new fish.