Goldfish produce a high bioload, which means their waste products build up rapidly, even in large tanks. What Does My Goldfish’s Tank Need? Filtration Image Credit: Andrey_Nikitin, Shutterstock What this doesn’t mean is that you should keep your goldfish in a 1-gallon bowl its entire life, but it does mean that your small goldfish is extremely unlikely to reach 12 inches in length in a 5-gallon tank. The more goldfish you have in a given space, the higher these hormone levels will be. Goldfish release some types of growth-inhibiting hormones, which build up in the water and, essentially, tell your goldfish’s body to stop growing. Interestingly enough, science tells us that’s mostly true. You may have heard that goldfish will only grow to the size of their environment. If you just adopted a 10-year-old goldfish from your friend’s pond, then you’re probably dealing with a fish that is much too large for a 10-gallon tank. If you just got a feeder goldfish from the fair or pet store, then your fish will be perfectly happy in a tank smaller than 10 gallons. The simplest answer to this question is that tank size isn’t as important as other aspects of tank care are. How Important is Tank Size for Goldfish? Image Credit: Sad Agus, Shutterstock Here are the things you should know about the importance of tank size for goldfish.
The good news for you is that those “rules” are outdated and not based on science, but for some people, that makes it even more confusing to figure out what size tank to get for a goldfish. You may have even encountered people who accused you of abuse or encouraged you to get rid of your goldfish when they found out you’re keeping a goldfish in a 10-gallon tank. The two most common seem to be 1 gallon for every 1 inch of fish and 20 gallons for a single fish with 10 gallons added for each additional fish. Whether you’re new to the goldfish world or have been keeping goldfish for decades, you’ve likely heard some rule of thumb describing the tank size that goldfish require.