Here's why:
* Waste: Goldfish are messy eaters and produce a lot of waste, which contaminates the water. More water dilutes the waste, making it less harmful.
* Oxygen: Goldfish need oxygen to breathe, and the water needs to be properly oxygenated. Larger tanks have a larger surface area, allowing for more oxygen exchange.
* Space: Goldfish grow quite large, and they need space to swim and explore. A larger tank provides them with more room to live comfortably.
Important note: This is just a general guideline. The actual amount of water your goldfish needs will depend on the specific type of goldfish, their size, and the type of filter you're using.
It's always better to err on the side of too much water than too little. A larger tank will be healthier for your goldfish and make it easier to maintain their water quality.