Question: how many litres of water do you need for 2 goldfish?
Answer: What Size Is Appropriate for a Goldfish Tank? Get 20 gallons (75 liters) at the very minimum and only if you're keeping one or two goldfish. We'll get to why in a minute, but you don't want an aquarium smaller than that. Depending on how many goldfish you plan to keep, chances are you'll want a tank much, much larger.