Goldfish Tank Size Goldfish Tank Size is very important. In a small tank, water conditions can occur rapidly, while too large a tank can be a burden for a beginner. I recommend at least investing in a 10 gallon. Choose a tank that has more water surface and less depth. Rectangular ones are better suited for Goldfish. Goldfish tend to require more space than other varieties of fish. A Good Rule To Follow: 1 Fish Per 10-20 Gallons Of Water Dangers … [Read more...] about Goldfish Aquarium: Everything About Goldfish Tank