How Many Goldfish Can you Safely keep in a 30 & 35 Gallon Aquarium?

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Goldfish have been a popular pet fish for many years, especially with kids. In fact, I’m sure most of us have kept one of these beautiful fish at some time in our lives. 

There are over 200 different varieties of goldfish to choose from, all of which can grow to over 6 inches long. For that reason, goldfish need plenty of space to thrive.  

So, how many goldfish can live in a 30 and 35-gallon tank?

As a general rule of thumb, you should allow 1 to 2 gallons of water per inch of fish. Goldfish are very dirty fish, so be careful not to overcrowd your tank. These are highly social fish that need to live in groups to be happy and thrive, and luckily, you can keep three or four goldfish in a 30 to 35-gallon tank.

Keep reading to learn more about keeping goldfish in a 30 to 35-gallon tank.

Goldfish Need An Adequate Amount of Water!

Fantail goldfish

One of the most important things to remember when keeping goldfish is that they need an adequate amount of water. You should never put more goldfish in a tank than what the goldfish water tank can accommodate. A good rule of thumb is to allow at least 10 gallons per fish for each goldfish you plan to keep in the tank.

Given that a single fish can grow between 8- 10 to 10-12 inches in length, they will require a decent size fish tank that will give them ample space to grow and swim around.

Some aquarists may be hesitant about getting large tanks because of how much it costs to keep them heated. The good news is that goldfish are cold-water fish that can tolerate a wide range of temperatures. This means that you will not have to spend as much money on heating the tank as you would if you were keeping tropical fish.

30-35 Gallon Tank – How Many Goldfish Can You Have?

So, now that we know how much water each goldfish needs, we can answer the question – how many can you keep in a 30-35 gallons tank? The answer will depend on factors such as the variety of goldfish in question, but generally speaking, you can comfortably keep around 3-4 goldfish in 30-35 gallons of water.

A few factors can determine exactly how many goldfish you can comfortably keep in a 30-35 gallon tank. We will address some of them below.

What Affects The Number of Goldfish You Can Keep In A Tank?

There are a few factors that you need to consider when trying to determine how many goldfish you can keep in your tank. These include the following:

Goldfish Species

Remember that most goldfish species are fast-growing, so don’t be fooled by the cute tiddlers you bring home from the fish store!

All goldfish species are peaceful and get along well together. However, I would avoid keeping fancy goldfish with slim-bodied varieties, as the fancies are clumsy, slow swimmers that will probably be outcompeted at feeding times by the faster slim-bodied types and could also be bumped and barged if they get in the way.

Ideally, you should keep larger, faster goldfish varieties in a very large aquarium or garden pond.

The Shape of the Tank

contemporary look of an aquarium with stones, driftwood and an artificial plant
Image Source:

The shape of a goldfish tank may not matter if you’re housing a single comet goldfish, but if you’re planning on creating a school of fish, then the shape of your tank can play a more significant role.

For example, rectangular tanks tend to be better for housing goldfish because they provide ample space and fewer corners that are harder for the fish to maneuver around. Therefore, if you want to keep more goldfish in your tank, it is recommended that you opt for rectangular tanks over cylindrical or square tanks.

Every additional goldfish you keep in your tank will need more water and more space to swim. Therefore, if you want to keep a small school of 3 or 4 goldfish, it is best to go with a larger rectangular tank that can accommodate their needs. 

Decorations & Plants

Fish Tank Plants Decor

It is best to go with minimal décor to maximize the number of fish you can house in your tank. This is because having too many decorations can reduce the amount of space available for the fish to swim around. It can also create more hiding spots for uneaten food, quickly leading to water quality issues. A 35-gallon tank with minimal decorations will be a better option for goldfish than one filled with plants and other decorations.

If you want to add some decorations to your tank, it is best to go with live plants. This is because they will help oxygenate the water and provide a place for the goldfish to hide if they feel scared or threatened. However, you should note that adult goldfish are known to uproot aquarium plants and decorations when looking for food. So, if you want to keep live plants in your tank, it is best to go with hardy plants that can withstand the waste produced by goldfish.

well-decorated full-size goldfish tank will look better than a barren one. But, if you’re looking to maximize the number of fish you can keep in your tank, it is best to go with a more minimalist approach. Alternatively, you can always get a larger tank to accommodate more fish and decorations.

What Happens When You Overstock A Tank?

Now that we’ve gone over how to determine the number of goldfish you can keep in a 30-35 gallon tank, it is important to note what happens when you overstock a tank.

Water Quality Issues

The most common issue that arises from overstocking a goldfish tank is water quality. When you have too many fish in a tank, they produce a lot of waste products. In a tank that is too small for your fish, these waste products can quickly build up and lead to ammonia poisoning or other water quality issues.

Water quality issues can cause your fish to become sick and even die. Therefore, you mustn’t overstock your tank. If you notice that your water quality is starting to decline, it is essential to take action immediately to correct the issue. This may include doing more frequent water changes or adding a filter to your tank.

Ultimately, the best way to avoid water quality issues is not to overstock your tank. Make sure that you do your research to determine how many fish your tank can accommodate.

Stress & Disease

Sick goldfish with bumbs on its scale, fish bowl pet

Another issue that can arise from overstocking a goldfish tank is stress and disease. When the space requirement of your fish is not met, they will often become stressed. This stress can suppress your immune system and make your fish more susceptible to disease. You may notice their fins becoming frayed or their bodies turning white if they suffer from stress.

Goldfish are especially susceptible to stress because they are such social creatures. When they are not given enough space, they often become anxious, leading to health problems. Additionally, when fish are too close together, they can often nip at each other’s fins. This can cause damage to the fins and coats of goldfishes, which can lead to infection.

To avoid stress and disease, you should provide your fish with enough space to swim around and hide. This will allow them to feel secure and reduce their risk of becoming anxious or sick.


Ranchu goldfish

Another issue that can arise from overstocking a goldfish tank is aggression. When fish are overcrowded, they often become aggressive towards each other. This aggression can lead to fighting and even death. Goldfish are especially prone to aggression when they do not have enough space.

Therefore, when stocking your tank with goldfish, you need to ensure enough space for each goldfish to carve a safe zone to call its own. Otherwise, you may end up with a tank full of aggressive fish that are constantly fighting with each other. And, no one wants that.

So, now that you know the risks of overstocking a goldfish tank, it is important to stick to the recommended stocking levels for your tank. This will ensure that your fish are healthy and happy.

The Takeaway

Goldfish are social creatures that need plenty of space to swim around. When stocking a 30-35 gallon tank with goldfish, it is best to stick to 2-3 fish. You run the risk of overstocking your tank, leading to water quality issues, stress, disease, and aggression.

Of course, you should also consider the type of goldfish you are keeping. Some goldfish grow to be quite large and need a larger tank to accommodate their size. So, be sure to do your research before stocking your tank.

We hope this article has helped teach you how many goldfish you can keep in a 30-35 gallon tank. If you have any questions or comments, please feel free to leave them below. And, as always, happy fishkeeping!

Wanda is a second-generation aquarist from the sunny tropics of Malaysia. She has been helping her father with his freshwater tanks since she was a toddler, and has fallen in love with the hobby ever since. A perpetual nomad, Wanda does her best to integrate fish-keeping with her lifestyle, and has taken care of fish in three different continents. She loves how it provides a nice break from the hustle and bustle of life.

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