What Size Aquarium Should I Get – The Ultimate Guide To Choosing

Written ByHoward Parker

Choosing your first tank is an exciting milestone, but it is easy to feel overwhelmed by the endless options lining the shelves of your local fish store.

We have all been there, staring at rows of glass boxes and wondering if a small desktop setup is easier than a massive centerpiece.

In this guide, I will help you navigate the world of tank dimensions and volumes so you can start your hobby with total confidence.

One of the most common questions I hear from new hobbyists is, “what size aquarium should i get?”

We will explore everything from water chemistry stability and floor weight limits to the specific needs of the fish you dream of keeping.

By the time you finish reading, you will know exactly which tank size fits your lifestyle, your budget, and your aquatic goals.

The “Bigger is Better” Rule: Why Volume Matters

If you are a beginner, your instinct might be to start small to “test the waters,” but in the aquarium world, this is often a mistake.

Larger volumes of water are significantly more stable than smaller ones because toxins like ammonia and nitrite dilute more effectively in more water.

In a 5-gallon tank, a single piece of uneaten food can cause a massive spike in toxins that could harm your fish within hours.

In a 40-gallon tank, that same piece of food is a minor blip that the beneficial bacteria can easily handle without crashing the system.

When people ask what size aquarium should i get, I almost always recommend starting with at least a 20-gallon “Long” tank.

This size provides enough of a “buffer” to protect you from common beginner mistakes while remaining manageable for regular maintenance.

Critical Factors to Consider for what size aquarium should i get

Before you swipe your credit card, you need to evaluate the physical and logistical reality of keeping a glass box full of water.

The size of the tank dictates everything from the cost of your monthly power bill to the structural integrity of your living room floor.

Available Space and Floor Support

Aquariums are incredibly heavy; water weighs approximately 8.34 pounds per gallon, and that does not include the weight of the glass, substrate, and rocks.

A 55-gallon tank can easily weigh over 600 pounds once it is fully decorated and filled, which is like having three grown men standing on one spot.

Always ensure the floor where you plan to place the tank is level and structurally sound, especially if you are looking at tanks over 75 gallons.

The Cost of Equipment and Maintenance

When you increase the size of the tank, the cost of everything associated with it scales up as well.

A 10-gallon tank needs a small, inexpensive heater and filter, whereas a 125-gallon tank may require dual canister filters and high-wattage heaters.

Don’t forget the cost of substrate; filling a 4-foot tank with high-quality aqua-soil can cost significantly more than the tank itself.

Your Personal Schedule

Think about how much time you can realistically dedicate to weekly water changes and glass scrubbing.

While larger tanks are more chemically stable, a 50% water change on a 100-gallon tank involves moving 50 gallons of water, which takes time and effort.

If you have a busy lifestyle, a well-balanced 20 or 29-gallon tank might be the perfect “sweet spot” for your home.

Understanding Tank Footprint vs. Vertical Height

Not all gallons are created equal, and the shape of the tank is often more important than the total volume.

When deciding what size aquarium should i get, you must look at the footprint, which is the surface area of the bottom of the tank.

The Importance of Surface Area

Oxygen exchange happens at the surface of the water, meaning a long, shallow tank has better gas exchange than a tall, narrow one.

Fish also tend to swim horizontally rather than vertically, so a 20-gallon “Long” tank offers more swimming room than a 20-gallon “High” tank.

If you plan on keeping active swimmers like Zebra Danios or Neon Tetras, horizontal space is your best friend.

Tall Tanks and Specialized Species

Tall tanks are visually stunning and work well for species that like to hang out in different water columns or have deep bodies.

Angelfish and Discus thrive in taller tanks because their long fins need the vertical clearance to prevent stress and stunted growth.

However, keep in mind that tall tanks are harder to clean because you have to reach deeper to vacuum the gravel or trim plants.

Matching Tank Size to Your Desired Fish Species

The most important factor in choosing a tank is the biological needs of the animals you want to keep.

Every fish has a minimum requirement for space to prevent aggression, promote growth, and ensure a long, healthy life.

Nano Tanks (5 to 15 Gallons)

These are perfect for shrimp colonies, snails, or a single Betta splendens, provided you are diligent with maintenance.

Avoid putting active schooling fish in these sizes, as they will feel cramped and may jump out of the tank due to stress.

Community Tanks (20 to 55 Gallons)

This is the most popular range for a reason; it allows for a diverse mix of species like Gouramis, Corydoras, and Livebearers.

A 40-gallon breeder is widely considered the “perfect” tank by experts because of its deep footprint and manageable height.

Large Predator or Cichlid Tanks (75+ Gallons)

If you are dreaming of Oscar fish, African Cichlids, or Goldfish, you cannot go small.

Goldfish are surprisingly messy and produce a large bio-load, requiring at least 20-30 gallons for the first fish and 10-20 for each additional one.

When you are deciding what size aquarium should i get, always research the “adult size” of the fish, not the size they are at the pet store.

The Hidden Benefits of Large Aquariums

While the initial setup cost is higher, large tanks offer a level of “forgiveness” that small tanks simply cannot provide.

In a large tank, the Nitrogen Cycle is much more robust, and the water chemistry stays consistent over long periods.

Lowering the Risk of Algae Blooms

Small tanks often struggle with rapid fluctuations in nutrients and light, which can lead to explosive algae growth.

Larger systems distribute nutrients more evenly, making it easier to maintain a crystal-clear display with less frequent “emergency” intervention.

Creating a Natural Ecosystem

A larger tank allows you to create a more complex hardscape with driftwood, rocks, and various plant species.

This extra room creates “micro-habitats” where shy fish can hide and dominant fish can establish territories without hurting others.

The result is a much more peaceful and naturally behaving community of fish that are a joy to observe.

Budgeting for Your New Setup

Let’s talk numbers, because the price tag on the glass is only a small portion of the total investment.

For a standard 29-gallon setup, you should expect to spend roughly 3 to 5 times the cost of the tank on accessories.

  • The Stand: Must be rated for aquarium use (particle board desks will sag and break).
  • Lighting: Essential for live plants; prices vary based on intensity and features.
  • Filtration: Aim for a filter that turns over the water volume 4-6 times per hour.
  • Substrate: Sand, gravel, or specialized soil for planted tanks.
  • Heating: A reliable, adjustable heater to keep tropical fish at 78°F.

If your budget is tight, look for “Dollar Per Gallon” sales or check local marketplaces for used setups, but always leak-test used tanks before bringing them inside.

Frequently Asked Questions (FAQ)

Is a 10-gallon tank good for a beginner?

While 10 gallons is a common starting point, it is actually harder to maintain than a 20-gallon tank.
The smaller volume means water quality can decline rapidly, so I recommend it only if you are committed to weekly testing and water changes.

Can I put a large tank on my second floor?

Most modern homes can support a 55-gallon tank on a second floor if placed against a load-bearing wall.
For anything 75 gallons or larger, it is wise to consult a structural engineer or check the direction of your floor joists.

Is there a standard answer for what size aquarium should i get?

There is no “one size fits all,” but the general consensus among experts is that a 20-gallon Long or a 29-gallon tank is the best entry point.
These sizes offer the best balance between ease of maintenance, cost, and the variety of fish you can successfully keep.

Does tank size affect how fast fish grow?

It is a myth that fish only grow to the size of their tank; instead, small tanks stunt their growth and cause internal organ damage.
Always choose a tank size based on the fish’s maximum potential adult size to ensure they remain healthy.

Acrylic vs. Glass: Does it matter for size?

For smaller tanks, glass is usually cheaper and more scratch-resistant.
For very large tanks (over 150 gallons), acrylic is often preferred because it is lighter and stronger, though it scratches easily.

Conclusion: Making Your Final Decision

Choosing the right aquarium is the foundation of your success in this rewarding hobby.

Don’t be afraid to go a little larger than you initially planned; you will rarely regret having more space, but you will almost certainly regret going too small.

Ultimately, the answer to what size aquarium should i get depends on your space, your budget, and the specific fish you want to keep.

Take your measurements, check your floor’s strength, and pick the largest tank that fits comfortably within your means.

Your future fish will thank you for the extra swimming room, and you will enjoy a much more stable and beautiful aquarium!

Happy fish keeping, and welcome to the wonderful world of Aquifarm!

Howard Parker
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