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Goldfish Tank Size Guide: Does Size Matter?

Gregory Iacono

By Gregory Iacono

planted goldfish tank

Although the most common pets in America are undoubtedly dogs and cats, you may be surprised to learn just how many people keep fish. According to a recent survey, an impressive 11.8 million US households own freshwater fish!1 Freshwater fish like goldfish are insanely popular, surprisingly tough, and come in various sizes and colors.

If you have plans to keep a goldfish or two as a pet, you probably want to know how large the tank should be. You might also wonder if tank size matters when it comes to goldfish. You should get at least a 10-gallon tank for one goldfish and if you plan to have more than one, add 10 gallons more for each.

That’s because, yes, tank size does matter. Some goldfish will grow quite large; others need their space because they’re territorial, so a larger tank is essential. Lastly, goldfish are remarkably active and need as much space as possible to be happy, healthy, and thrive.

There’s more to the goldfish tank size question, like what can happen if the tank is too small, can you put different goldfish species together in one tank, and how do you keep their tank water clean? If you’d like to know the answer to these questions and several more, plus get some interesting, actionable info about keeping goldfish in your home, read on!

Why Does Tank Size Matter for Goldfish?

The image of a goldfish in a bowl is indelibly imprinted on most humans’ brains. We see goldfish living like this in TV shows, movies, famous paintings, magazines, and more. Cleo, the flirty goldfish in Disney’s Pinocchio, is a prime example. As ubiquitous as this goldfish image might be, it’s also the worst way to keep them.

There are several reasons why including:
  • Goldfish are very active and need lots of space to swim around.
  • The amount of oxygen in a small tank will be far less than your goldfish needs to survive.
  • Harmful ammonia from goldfish poop will build up incredibly fast in a tiny bowl.
  • A small container can shorten a goldfish’s life significantly.
  • You can’t put a water filtration system in a tiny fishbowl.

As you can see, putting a goldfish in a bowl is more or less a death sentence. Most goldfish in bowls don’t live past 2 or 3 weeks, which is why there are so many “jokes” in shows and movies about having to flush the poor things down the toilet.

Goldfish-and-snail-in-aquarium-tank
Image Credit: dien, Shutterstock

How Do I Choose the Correct Tank Size for my Goldfish?

Choosing the correct tank size for one or more goldfish isn’t complicated. The rule of thumb is to have 1 goldfish for every 10 gallons of water. If you want, for example, 3 goldfish, get a 30-gallon tank. 5 goldfish? 50-gallons, and so forth.

What Influences a Goldfish’s Health More, Tank Size or Water Quality?

While there’s a lot of debate about what size is best for keeping goldfish, one factor is slightly more important if you want your goldfish to stay happy and healthy: water quality.

The fact is, you could put a single goldfish in a 50-gallon tank, and it would still suffer and die if the water in the tank is dirty. Yes, a tank large enough to provide ample swimming space for your Goldies is important. However, if they don’t have clean water, the tank size isn’t going to save them.

That means you need to clean the water regularly and have an excellent water filtration system in your tank. Live plants are also a great idea and will keep the water clean and reduce the need to change the tank’s water, which can take a lot of time and energy.

Can Different Goldfish Species Live Together in the Same Tank?

One of the questions asked most by goldfish enthusiasts is, can you put different goldfish species together in the same tank? There are over 200 types of goldfish! The answer is that you can put different types of goldfish together, but they should be more or less the same size and have the same propensity for swimming. Slow swimmers with slow, fast with fast, etc.

Goldfish that are significantly different in size and swimming habits might compete for food and space, which could get ugly. Nobody wants to see their fish fight.

Can Baby and Adult Goldfish Live in the Same Tank?

It’s best to keep baby goldfish in a separate tank from adults because, under most circumstances, the adults will eat the babies. You will be able to put the two together at a certain point.

Usually, that’s when the baby goldfish have become strong swimmers (so they don’t get sucked into the filter) and when they’re too big to fit in the adult goldfish’s mouth (so they don’t get eaten).

comet_goldfish
Image Credit: kaori, Pixabay

Is It Better To Have Multiple Goldfish in the Same Tank?

While you can put more than one goldfish in a tank that’s big enough, it’s not necessary for their health and well-being. Goldfish aren’t schooling fish and, in the wild, usually stick to themselves unless it’s mating season. Having a single goldfish in a tank is no problem and is preferred by most goldfish. Of course, having several goldfish is preferable to most humans because there are more of them to see and enjoy. ave divider ah

How To Keep the Water in a Goldfish Tank Clean

Earlier, we discussed how water quality is just as crucial as tank size. For that reason, we’ll look at how to clean the water in your goldfish tank. There are several excellent methods, most of which can be done once the tank is up and running.

1. Cycle the Goldfish Tank First

Cycling a fish tank should be done for all fish, including goldfish. Cycling means setting up your tank and letting everything run for a few weeks before adding your goldfish. For freshwater fish like goldfish, 3 to 4 weeks of cycling is a good idea. That way, the filter will be ready, “good” bacteria will form in the water, and the temperature will be just right.


2. Choose a Quality Biological Filter

The filter system you choose for your goldfish tank is critical. It needs to be rated for the number of gallons in your tank and, if possible, should be rated for about 20% more. (See our article on the 10 Best Filters for Small Aquariums if you need help choosing.)


3. Purchase a Siphon

A siphon is more or less a vacuum cleaner for a fish tank. You can use it as often as necessary to “vacuum” the fish poop and other debris out of your tank.

Siphon-gravel-cleaner-tool_Dmitri-Ma_shutterstock
Image Credit: Dmitri Ma, Shutterstock

4. Change 25% of the Tank’s Water Monthly

To get rid of the ammonia excreted by your goldfish in their tank, remove 25% of the water and replace it with fresh water once a month.


5. Place Live Plants in your Tank

Live plants not only look beautiful in a fish tank but also filter the water by removing ammonia, carbon dioxide, and nitrates. They also aerate the water by releasing oxygen (and do it better than a bubbler). Live plants also keep algae growth under control, which keeps your goldfish healthier and reduces the time you need to clean your tank.

Final Thoughts

Does size matter when it comes to goldfish tanks? Yes, because goldfish need plenty of water to swim, live and thrive. That makes tank size critically important for your goldfish.

However, as we’ve seen today, water quality is just as important as size. A large enough tank and ideal water quality are essential for keeping your goldfish healthy and ensuring they live a long life. The rule of thumb for tank size is 10 gallons for each goldfish, but you can modify it slightly as long as the water is kept clean.

We hope the information we’ve provided today has been helpful and given you the answers you were searching for. Keeping goldfish is a rewarding pastime and provides a soothing, tranquil respite from the stress of the modern world. However many goldfish you decide to keep, we wish you the best and hope your Goldies live long healthy lives!


Featured Image Credit: S-F, Shutterstock

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