How Many Fish in a 30-Gallon Tank? Guidelines for Aquarium

If you’re a beginner aquarist or are considering a new fish tank, you might be wondering “How many fish can I put in my 30-gallon aquarium?” The answer may depend on the types of fish and their ideal water conditions.

Though it’s important to take these factors into consideration, we can still provide a general answer to your question.

In this article, we’ll look at how many fish can comfortably live in a 30-gallon aquarium. We’ll examine the recommended stocking limit of different types of fish and which species are good for beginners.

How Many Fish in a 30-Gallon Tank

How To Calculate How Many Fish You Can Add to a 30-Gallon Tank?

Figuring out how many fish to add to a 30-gallon tank can be tricky. The one-inch per gallon rule of thumb has become the standard, but there are a few flaws in this standardized approach. Namely, it doesn’t take into account the size and type of fish, plants, decorations, or other factors that may affect stocking levels.

When calculating how many fish you can add to a 30-gallon tank, always factor in the size as well as the species of the fish that you plan on having. For example, you won’t be able to put four shark fishes together in one 30-gallon water tank; but if neon tetras are your chosen species you could fit up to 15!

It’s also worth checking out popular ‘how many fish in a tank calculators’ which can help accurately determine stocking levels depending on your desired fish species. When done properly, this formula accounts for more than just the size of your aquarium – it takes into account compatibility between species and other factors like aquatic plants and decorations too!

No. of Fish In 30-Gallon Water Tank

When it comes to stocking your 30-gallon water tank, knowing how many fish you can safely place in the space is key. This can range depending on the type of fish, but a general rule of thumb is one inch per gallon. Depending on the species of fish, this number may need to be modified.

For cichlids, which come in various species and colors, you can keep anywhere from four medium-sized cichlids to six dwarf African cichlids. As these are larger fish, any larger than this should not be kept in a 30-gallon tank.

Goldfish only require 10 gallons of water per fish meaning that only three could be safely kept in the tank. Guppies reach sizes between 0.6-2.4 inches meaning ten to 12 could be held in your 30-gallon tank, as well as 15 tetras who barely grow more than 1-2.5 inches respectively.

Alternatively, dwarf gouramis need 8-10 for a 30-gallon tank with their 2.5-4.5 inch size capacity while mollies need even more with an ideal 10-gallon capacity due to their 3.5-4.5 inch size and 72-78℉ temperature preference.

Furthermore, rainbowfish require 15-30 gallons of space due to their 3–7 inches size potential while angelfish has a minimum 20 gallon recommended due to their 6–8 inch max intake

The table shows the number of fish that can live in a 30-gallon tank and their sizes.

Type of FishSize Range in InchesFish in a 30-Gallon Tank
Molly0.5 -44-6
Angelfish5 – 121-2
Cory catfish1-49-11
Bristlenose plecos3-53-5
Cherry barbs1-210-12
Kuhli loach3-47-9

To accurately determine the number of fish in a given volume, you must take into account factors like size and species, then use the one-inch-per-one-gallon formula.

We can rule out that the number of fish will be approximately 3-4 times less than the per inch per gallon of water.

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Factors Affecting the Number of Fish Per Gallon

When setting up your aquarium, it’s important to consider the number of fish that can be safely put in it. This is something every tropical fish keeper needs to think about, as there are a few factors that influence this number and these need to be taken into account.

Size of Fish

The size of the fish you put in your aquarium can have a major influence on the number of fish you should add per gallon. Different species may grow to different sizes, so it’s important to take into account the estimated full-growth size when selecting which types of fish to keep in your tank.

Additionally, some fish can grow faster than others, so keeping an eye on the growth rate is key for knowing when you need to reduce stocking levels. Depending on these factors, the ideal number of fish for any given tank may vary.

Swimming Space

When deciding how many fish to put into your tank, swimming space should be a major factor. Different fish have different requirements for space, as some need more room than others. For example, Tiger Botia is active and requires more swimming room than other species, while others like Bettas may be content just to rest on the bottom or float near the surface.

It is also necessary to consider the type of swimming style of the fish – Anguilliform, Sub-carangiform, Carangiform, Thunniform, or Ostraciiform – and what layer they tend to swim in (top, middle, or bottom). If a tank is too small to meet all of these requirements then it can result in an unhappy experience for the inhabitants. So when considering how many fish to add to your tank, bear in mind their swimming space needs!

Waste Load

When it comes to stocking your aquarium, it’s important to consider the waste load that each fish species produces. Certain types of fish, such as Goldfish and Guppies, produce a lot of waste which can increase ammonia and nitrite levels in the water if not taken care of properly. Other types of fish, such as bettas, produce far less waste and are therefore better suited for smaller tanks.

Whichever fish you choose for your tank, it is essential that you account for their waste production when deciding how many fish to stock per gallon. By doing so, you can prevent an overload in ammonia and nitrite levels that could make the environment unfavorable for your aquatic friends!

Filtration System

Having a good filtration system for your aquarium is essential to the health and safety of your fish. It works by helping remove waste products from the water, making it cleaner for the aquatic life in your tank.

But it’s also important to ensure that your filter system is working properly and can keep up with the number of bacteria, including beneficial bacteria, you find in a tank. You’ll want to make sure it meets the needs of both the number and type of fish you have.

Otherwise, you may need a stronger filter that can handle more volume – like if you had 30-gallon water instead! Ultimately, the right filtration system will be based on what type and how many fish are in your aquarium.

Aquarium Plants

Aquarium plants play a crucial role in maintaining a healthy environment for your fish. Not only do they help keep the water clean and free of waste, but they also provide oxygen for the fish to breathe as well as offer protective hiding places for shy or timid species.

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When it comes to deciding how many plants should go into an aquarium, it’s important to note that this number will vary depending on the type of fish living in it and their individual needs.

While there are general guidelines that can be used for rough estimation purposes, you should always consider the number of plants you have in the tank when determining how many fish you can safely have per gallon.

Surface Area

When it comes to stocking the right number of fish in an aquarium, the amount of surface area the water has is one of the most important factors. That’s because the greater the surface area, the more efficient gas exchange with both oxygen and other pollutants will be – and therefore, more fish can be supported.

For example, a tank that is short and wide may have the same gallon capacity as one that is tall and thin – but it will support fewer fish due to less surface area for gaseous exchange.

The general rule of thumb is that each inch of a fish should fit under 12 square inches of surface area. However, this doesn’t always ring true – especially when you consider broader-bodied fish which need 20 square inches per inch instead.

Water Temperature

When setting up your tank, it is important to take the water temperature into account when deciding how many fish per gallon. The warmer the water, the less oxygen it can hold, which means that if too many fish are in a tank, they will quickly run out of oxygen and suffocate.

Therefore, it is important to consider both water temperature and the amount of oxygen needed by your fish when making stocking decisions for your aquarium. Having a low-temperature or well-aerated tank can ensure that your fish stay healthy and happy while avoiding any potential risk of them overcrowding or suffocating.

Aggression level of fish

For any aquarist, having an understanding of the aggression levels of different fish is indispensable.

When stocking your aquarium, it is important to consider the proper ratio of fish that can live in peace and harmony together. Some fish, like betta for example, are more territorial by nature and require ample space for each individual fish if they are to live together.

Cichlids on the other hand are a bit more aggressive and have higher levels of aggression. Thus, when stocking your aquarium it’s best to take into account their aggression level so as not to overcrowd or hurt any of its inhabitants.

Aquarist Management

The number of fish per gallon in an aquarium is determined largely by the aquarist’s management of the tank. Aquarists, as the governing factor, need to carefully consider how many fish will be in their tanks and take into account all relevant factors.

The bioload increases with more fish, meaning that water changes and adequate filtration are necessary for keeping water quality high. An inexperienced aquarist may not be able to keep up with the demands of a heavily populated tank, resulting in fewer fish overall.

It’s important for aquarists to do their research and plan ahead when stocking a tank in order to have a healthy, successful aquarium.

How Much Water Is In A 30 Gallon Fish Tank

If you’ve recently gotten a 30-gallon fish tank, you might be wondering how much water you need to fill it up. According to our calculations, a 30-gallon fish tank with dimensions of 80cmx40cmx35cm needs roughly 25 gallons of water. That equals about 212 lbs when the tank is full.

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If your 30-gallon fish tank is made out of glass, it will weigh an additional 45 pounds when full, making the total weight of the tank 262 lbs. This means that it’s safe to place the tank on residential floors since they are built to hold up to 200 kg per square meter.

To be sure that your tank has the right amount of water in it, we suggest using a weighing machine to accurately measure its capacity. This way you can make sure that your fish stay healthy and happy!

Benefits Of A 30 Gallon Fish Tank

A 30-gallon fish tank is an excellent choice for aquarium lovers of all types, and especially for beginners. The size of this aquarium gives you more freedom to select a variety of species and decorations. When it comes to pricing, a smaller tank is usually much more affordable and easier to stock than larger tanks, so if you have a limited budget then this size should be your first choice.

Maintaining a 30-gallon tank is also easier than with larger models since it only requires regular water changes (approx 20%) as well as frequent testing and the usual checks on equipment. Plus, they come in many different styles and shapes which means they can fit into almost any space.

Finally, they are ideal for those who want to challenge themselves by trying to breed their own species – making them perfect for breeder tanks despite their small size!


Which Fish Varieties Can Not Live Together in a 30-Gallon Water Tank?

Certain shark, mormyrid, and knife fish species, as well as other territorial and aggressive varieties, are not compatible with a 30-gallon water tank. Unlike guppies and neon tetras, they require more space in order to cohabitate peacefully.

Can Two or Three Goldfish Live in a 30-Gallon Tank?

When choosing a tank for goldfish, it is recommended that two or three be housed in a 30-gallon tank, although a bigger size is preferable to give the fish more space to swim. This helps keep the fish healthy and content.

Can Guppies Stay with Neon Tetras in a 30-Gallon Tank?

Ready to give guppies and neon tetras a chance to become buddies? They can peacefully dwell in a 30-gallon tank! Just remember, they’re social little fish so be sure to introduce a minimum of two-three guppies and six neon tetras for maximum harmony.

How Many Tetras Should Be Together?

Neon tetras are schoolers, so it is recommended to house them in groups of at minimum six fish in order for them to form their own community.

What Are Fish Breeds That Live Well Together?

Get connected with community fish! These vibrant creatures will be perfect additions to your tank – guppies, gouramis, tetras, mollies, loaches, catfish, corys, danios, platies, plecos, rasboras, and swordtails are just a few on the list.

What Fish Can You Not Put Together?

Got territorial fish? Some species, like sharks, knife fish, Cichlids, mormyrids, and other almost possessive finned friends won’t share their space – so keep ’em separate!


Keeping fish in a 30-gallon tank can be a great way to bring the beauty and serenity of fish into your home. There is no exact right or wrong answer when it comes to how many fish you can keep in such an aquarium, however, you should always prioritize the health and safety of any aquatic creature.

Set up your tank properly so that it has adequate filtration and decor, do your research on compatible species, and monitor ammonia levels often to ensure that all members of your tank are happy and healthy.