Best Size Fish Tank for Beginners – Ultimate Guide

Welcome to the wonderful hobby of fishkeeping! But wait, before you start picking out fish and tank decor, there's one important decision you need to make: what size fish tank should you get? Based on my experience I'll help you pick the best sized tank for your needs. So, grab a cup of coffee (or tea, if that's your thing), and let's dive in!
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As you’re here you’ve obviously asked the question what is the best size fish tank for beginners?

Well, in my experience, it all depends on what fish you’re looking at keeping.

If you’re wanting to keep a betta fish, go with a 5 or 10-gallon tank.

If you’re wanting to keep a 1 small goldfish, a species-only tank, or a community tank with various species, then go with a minimum tank size of 20 gallons.

A 20-gallon tank is large enough to be able to create a great display tank without being too difficult to maintain and you can great 20 gallon fish tank kits for a reasonable price.

But, before you go ahead and order a tank, take the time to read this entire best size fish tank for beginners post as it covers:

  • Why Tank Size Matters
  • Things You Need To Consider
  • Dispelling Common Misconceptions
  • Best Tank Kits For Beginners
  • 20 Gallon Tank Stocking Ideas

You’ll then have everything you need to consider so you can make an informed decision when purchasing your fish tank.

Why Tank Size Matters

You need to have the right-sized tank for the fish you’re wanting to keep.

Different fish species have different requirements for their aquatic habitat, such as the amount of space they need to swim, the amount of oxygen they require, and the water conditions they prefer.

Some fish don’t grow too much from the size you buy them in the pet store, others grow very quickly to a large size.

Some fish species are more active and require more space, while others are more docile and can thrive in smaller tanks.

It is important to research the specific fish species you want to keep and choose a tank size that can accommodate their needs.

Things You Need To Consider

When choosing the best size fish tank for beginners, there are several things to consider.

Space and Budget

The first thing to consider when choosing a fish tank is the space you have available in your home. You want to choose a tank that fits comfortably in your space and doesn’t overwhelm the room.

Additionally, you need to consider your budget. Larger tanks can be more expensive, so it’s important to choose a size that fits your budget.

Fish Species & Quantity Of Fish

The type and number of fish you plan to keep will play a role in determining the size tank you buy. Do you want a single fish tank or a community tank?

Some fish species require more space than others. For example, larger fish like cichlids and angelfish need more room to swim than smaller fish like tetras and guppies.

Water temperature, pH level, and water hardness are all things you need to take into account.

Research the specific needs of the fish you plan to keep to determine the appropriate tank size and if they are compatible with each other if you want a community tank.

Betta fish and goldfish are a great example of incompatible tank mates (you wouldn’t believe how many people try to house these fish together!), whereas betta fish and rummy nose tetras can get along harmoniously (with the right conditions).

Heaters and Filters

Larger tanks require larger heaters (if you want to keep tropical fish) and filters to keep the water at the appropriate temperature and quality.

Make sure you choose the appropriate equipment for the size of your tank.

I use the Fluval 07 range of filters, as they are reliable and well-built.

Plants and Decor

Amazon Sword
Java Fern

Finally, consider the plants and decor you plan to include in your tank. Larger tanks provide more space for plants and decorations, which can create a more natural and visually appealing environment for your fish.

Plants are also a great way to help with removing toxins from your tank water. But, keep in mind that plants and decor also take up swimming space for your fish, so it’s important to strike a balance.

If you’re looking for low-maintenance plants for your tank, some great choices are:

  • Amazon Sword – needs substrate, provides hiding places
  • Anacharis – no substrate required, easy to care for
  • Java Fern – no substrate required, easy to care for
  • Pothos – leaves grow outside of the aquarium so offers something different aesthetically

Dispelling Common Misconceptions

Facts vs Myths

There are several misconceptions you need to be aware of as a new fish keeper.

A Small Fish Tank Is Easier To Maintain Than A Larger Tank

Fake News

If you haven’t owned an aquarium before, it’s natural to think that a smaller tank will be easier to take care of than a larger tank.

When you set up your fish tank, you’re creating an ecosystem that you have to maintain to keep your fish happy and healthy. 

Fish produce waste. Like us, they have to eat, and what goes in one end comes out of the other end. Fish poop breaks down and releases ammonia and other toxins into the water.

A larger tank can accommodate more water which dilutes the waste produced by the fish. This means that the water quality is easier to maintain, and your fish are less likely to get sick or stressed.

Smaller tanks are less stable and more prone to fluctuations in water quality. This means that you’ll need to be more vigilant when it comes to testing the water and performing water changes.

Fish Are Easy Pets That Require Little Attention


While fish may not require as much care as other pets, such as a dog or a cat, they still need a clean and healthy environment to thrive.

This means that you’ll need to invest time and effort into maintaining your fish tank, including regular water changes and filter cleanings.

Fish Only Grow To The Size Of Their Tank


While there is some truth to this, it’s really not good for your fish.

What actually happens is your fish don’t have enough space which stresses them. This stress releases hormones through their body which stunts their growth.

Besides stunted growth, a stressed fish also has a suppressed immune system which can leave them vulnerable to parasitic infections such as:

When I won my first goldfish Moby at the fair, I bought a small fish bowl for him as I didn’t know any better. Once I realized this was far too small for him I felt terrible and upgraded him to a 20 gallon tank.

You Can Add As Many Fish As You Want


Overstocking a tank is a common mistake that many beginners make, including me when I first started out!

Fish produce waste. More fish = more waste. Too much waste can quickly accumulate in the water and create an unhealthy environment.

Overstocking your tank can lead to a variety of problems, including disease, aggression, and ammonia spikes.

I advise consulting a reliable aquarium stocking calculator to help you avoid this problem.

Owning a fish tank does require a certain amount of knowledge, including understanding the nitrogen cycle and water chemistry, but it’s not that hard. If I can learn it, so can you.

Best Complete Tank Kits For Beginners

In this section, I’ll take you through some great tank starter tank kit options.

These starter kits are great as they contain everything you need to get you going.

Bear in mind the included accessories you get with them are there to do just that; to get you started.

Once you’ve been bitten by the bug of this hobby (believe me, it’s super addictive!) you may choose to upgrade them at some point in the future.

Aqueon 10 Gallon Fish Tank Starter Kit

Made in USA Decorations not included
High-quality scratch-resistant glass Substrate not included
Easy to set up and maintain Some customers complain the filter is noisy
Filter included Heater temperature can’t be adjusted
Heater included
LED lights included
Excellent customer service from Aqueon

The Aqueon 10 Gallon Starter Kit has all the equipment you need to get started in one convenient box.

This is the only 10-gallon aquarium kit that comes with a heater included

The tank dimensions are: Width 20.25 inches x Depth 10.5 inches x Height 12.6 inches

The full kit includes:

  • USA made 10-gallon glass aquarium
  • Low-profile lid with built-in LED lights
  • Aqueon 10 QuietFlow power filter
  • Filter cartridge
  • Submersible preset heater
  • Premium fish food sample
  • Water conditioner sample
  • Fish net
  • Thermometer
  • Setup guide

All you need to do is add your favorite style of plants and decor to customize your tank.

The preset heater will keep your aquarium temperature at a constant 78° F, which is appropriate for most tropical fish. But if you want a heater with an adjustable temperature the 50 Watt Aqueon Submersible Heater is ideal for this tank size.

There are a few customers complaining about the filter being noisy, but the Aqueon Quietflow filter I got with my kit has been very quiet, so it’s probably down to potluck with that.

The filter has a red LED light that flashes to indicate when it’s time to change the cartridge which takes away some of the guesswork.

You should replace them with Medium Aqueon Replacement Filter Cartridges for optimal performance.

All in all, a great value starter kit for a beginner.

If you’re looking for the best betta fish tank with filter and heater included, look no further.

Aqueon 20 Gallon High Fish Tank Starter Kit

The Aqueon 20 Gallon High Starter Kit comes with all the same specs as the 10 gallon above, it’s just larger and gives you the option of keeping more fish.

The tank dimensions are: Width 24.25 inches x Depth 12.5 inches x Height 16.75 inches

Tetra Aquarium 20 Gallon Fish Tank Kit

Made in USA Decorations not included
High-quality scratch-resistant glass Substrate not included
Easy to set up and maintain Heater temperature can’t be adjusted
Filter included
100 watt heater included
LED lights included

The Tetra 20 Gallon Fish Tank Kit is made in the USA and built to last with scratch-resistant glass.

Tank dimensions are: Width 24 inches x Depth 12 inches x Height 16 inches

The Tetra Kit includes:

  • 20-gallon glass aquarium
  • Lid with built-in LED lights
  • Tetra mini UL heater
  • Tetra Whisper 20 filter
  • Artificial boxwood plant mat
  • Four artificial plants 

The aquarium comes with an LED hood that provides a natural daytime effect and a Whisper Filter that is (as the name suggests) whisper quiet while providing powerful, dependable water flow.

As with the Aqueon kits above, the 100 watt heater is preset and will keep your water at approx 78° F and isn’t adjustable. Again, if you want a heater with an adjustable temperature the 50 Watt Aqueon Submersible Heater is ideal for this size of tank.

All you need to do is add, water, gravel, and fish to complete your aquarium.

20 Gallon Fish Tank Stocking Ideas

Stocking Ideas For 20 Gallon Tank

There are tons of options when it comes to fish that are suitable for 20-gallon tanks, it would be impossible to list them all, but here are some great options to get you started.

For a 20-gallon single fish tank, you could choose:

For a 20 gallon species only tank you could look at:

Some great 20 gallon community tank stocking ideas are:

Option 1:

  • 1 Dwarf gourami (Female)
  • 5 Cherry barbs
  • 3 Guppies
  • 4 Corydoras catfish

Option 2:

  • 1 Yellow dwarf cichlid
  • 6 Glowlight tetras
  • 3 Platties
  • 1 Clown pleco

Option 3:

  • 1 Kribensis cichlid
  • 8 Von Rio tetras
  • 6 Otocinclus catfish
  • 6 Endler’s livebearers (same sex – they breed quickly!)

See my best freshwater fish, best algae eating fish, and best fish for a 3 gallon tank articles for more fish stocking ideas and inspiration.

Closing Thoughts On The Best Size Fish Tank for Beginners….

To quickly recap the main things to consider when choosing your first fish tank are:

  • Buy the biggest tank that you have the space and budget for. It’s much easier to maintain the water quality in a larger tank than in a smaller tank.
  • Make sure you get a suitable heater and filter for the size of tank you choose.
  • Research the fish you’re looking at keeping and make sure they’re going to be suitable tank mates if you want to keep a community tank.
  • Don’t add too many fish at once, patience is the key!

Maybe you’ve got space for something larger than a 20 gallon tank, in which case you could consider a 37 gallon or 40 gallon breeder tank, which will give you a much bigger choice of fish that you can keep.

Check out the equipment section for more in-depth reviews and guides like this, and the aquarium health section for guides on keeping your aquarium in tip-top shape.

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Hey, fellow fish enthusiast 👋! I'm Paul and I've been an aquarium addict since I won my first goldfish at the fair many years ago. Let me share with you the knowledge that I've gained along the way (and avoid the mistakes I've made!), so you too can create an underwater paradise for your aquatic friends.