20 Gallon Hexagon Aquarium – The Ultimate Guide To A Stunning Vertical

Setting up a 20 gallon hexagon aquarium is one of the most rewarding ways to add a splash of nature to a tight corner of your home. These vertical tanks offer a unique aesthetic that traditional rectangular tanks simply cannot match, providing a 360-degree view of your aquatic world.

If you have been eyeing that tall, elegant glass prism at the local fish store, you are in the right place. While they look spectacular, hexagon tanks require a slightly different approach than standard setups to keep your fish healthy and your plants thriving.

Don’t worry—this setup is perfect for beginners and intermediate keepers alike! In this guide, I will walk you through everything from equipment selection to the best fish species, ensuring your vertical masterpiece becomes the focal point of any room.

The Unique Appeal of the 20 Gallon Hexagon Aquarium

The first thing you will notice about a 20 gallon hexagon aquarium is its footprint. Because it grows “up” rather than “out,” it fits perfectly on end tables, in office corners, or in small apartments where floor space is at a premium.

However, the shape changes the way water interacts with the environment. Before you dive in, it is helpful to understand choosing the right shape for your specific goals, as height affects everything from light penetration to gas exchange.

Understanding the Surface Area Challenge

In a standard 20-gallon “long” tank, there is a lot of room for oxygen to enter the water at the surface. In a hexagon tank, the surface area to volume ratio is much smaller, meaning there is less interface between the air and the water.

To keep dissolved oxygen levels high, you must prioritize water movement. This ensures that oxygen-rich water from the surface is constantly being pulled down to the bottom where your fish and beneficial bacteria need it most.

Maximizing Vertical Swimming Space

While some fish love to dart back and forth horizontally, others appreciate the vertical swimming space a hexagon tank provides. This height allows you to create distinct “zones” in your aquarium, with different species occupying the top, middle, and bottom layers.

By thinking vertically, you can turn a relatively small footprint into a lush, multi-tiered ecosystem. It is all about choosing the right inhabitants that feel comfortable moving up and down the water column rather than just side to side.

Essential Equipment for a Hexagon Setup

Because of the depth of a 20 gallon hexagon aquarium, your standard “off-the-shelf” equipment might need a bit of a tweak. You need gear that can reach the bottom of the tank and maintain consistent conditions throughout the entire vertical span.

Choosing the right tools from the start will save you a lot of headaches later. Let’s look at the three most critical pieces of hardware you will need for a successful tall tank.

High-Output Lighting for Deep Water

Standard LED hoods often struggle to send enough light to the bottom of a 24-inch tall tank. If you plan on growing live plants, you will need a light with good “PAR” (Photosynthetically Active Radiation) values to reach those bottom-dwelling species.

Look for LED fixtures specifically designed for deeper tanks. Without adequate light, your foreground plants will likely “stretch” toward the surface, becoming leggy and weak instead of forming the lush carpet or bush you desire.

Filtration and Aeration

An internal power filter is often an excellent choice for a hexagon tank because it can be placed lower in the water column to improve circulation. Alternatively, a strong hang-on-back filter with an extended intake tube works well to pull debris from the substrate.

To ensure your fish have plenty of oxygen, I highly recommend adding an air stone or a small sponge filter. This breaks the surface tension and helps with the gas exchange that is so vital in tanks with a narrow top opening.

Reliable Heating

Consistency is key when it comes to temperature. A high-quality submersible heater should be placed near the filter intake or outflow to ensure the warmed water is distributed evenly throughout the height of the tank.

In a tall tank, heat can sometimes trap at the top while the bottom remains cool. By placing your heater horizontally near the bottom or right next to a flow source, you prevent these “cold spots” from stressing your livestock.

Aquascaping for Height and Depth

Designing a 20 gallon hexagon aquarium is where the real fun begins! You aren’t just decorating a floor; you are building a mountain. The goal is to use the height to your advantage by creating a sense of scale and perspective.

Start with your hardscape. Large pieces of driftwood, like Manzanita or Spider Wood, can reach from the substrate all the way to the surface, providing “roads” for your fish to travel and places for you to attach epiphytic plants.

Choosing the Right Substrate

Since you’ll likely be planting heavily to fill that vertical space, a nutrient-rich soil or a high-quality fluorite gravel is a must. Ensure you have at least 2-3 inches of depth to anchor the roots of tall, heavy plants.

If you are unsure about the volume needed, you can check guides on choosing a high-quality filter and substrate to ensure you have the right foundation for your specific tank dimensions.

The Best Plants for Tall Tanks

To fill the background and midground, look for species that naturally grow long and flowing. Vallisneria spiralis (Italian Val) is a classic choice; its ribbon-like leaves will reach the surface and trail across the top, creating a beautiful “jungle” effect.

For a bold centerpiece, Echinodorus amazonicus (Amazon Sword) is hard to beat. Its wide, bright green leaves provide excellent cover. For the mid-level, consider attaching Anubias or Java Fern to your driftwood to fill in the “empty” middle space of the tank.

Best Fish Species for a 20 Gallon Hexagon Aquarium

When stocking a hexagon tank, you must avoid “high-energy” swimmers like Giant Danios or large Tetras that need long horizontal runs. Instead, focus on fish that hover, glide, or enjoy exploring nooks and crannies.

The 20 gallon hexagon aquarium is an ideal home for “centerpiece” fish that have a lot of personality. Here are my top recommendations for a balanced and beautiful vertical community.

The Centerpiece: Honey Gourami

The Trichogaster chuna, or Honey Gourami, is a peaceful, slow-moving fish that absolutely loves the stiller waters of a tall, planted tank. Their bright orange or yellow coloration pops beautifully against green plants.

Because they are labyrinth fish, they breathe air from the surface. The vertical nature of the hexagon tank makes it easy for them to swim up for a gulp of air and then drift back down to their favorite hiding spot among the leaves.

Middle-Dwellers: Endler’s Livebearers

Poecilia wingei, commonly known as Endler’s Livebearers, are small, incredibly active, and vibrantly colored. They tend to occupy the upper and middle portions of the tank, darting through the leaves of your tall plants.

They have a low bio-load, which is helpful in a tank with less surface area. A small group of males will provide constant movement and flashes of neon color without overwhelming the filtration system.

The Bottom Crew: Pygmy Corydoras

No tank is complete without a cleanup crew! Corydoras pygmaeus (Pygmy Cory) are unique because they don’t just stay on the sand; they often “perch” on plant leaves in the middle of the tank.

These tiny catfish are social and should be kept in groups of six or more. They will spend their days scavenging for leftover food, ensuring your substrate stays clean and your ecosystem remains balanced.

Stocking and Compatibility Table

To help you visualize a perfect setup, I have put together this quick-reference table. These species are selected specifically for their compatibility in a vertical 20-gallon environment.

Species	Tank Zone	Count	Expert Tip
Honey Gourami	Top/Middle	1-2	Provide floating plants for bubble nesting.
Endler’s Livebearers	Middle	6-8	Keep all males to prevent overpopulation.
Pygmy Corydoras	Bottom/Middle	6-10	Use soft sand to protect their barbels.
Amano Shrimp	All Zones	3-5	Excellent for controlling hair algae.

Maintaining Your Vertical Ecosystem

Maintenance on a 20 gallon hexagon aquarium can be a bit tricky due to the depth. You will likely need a longer-than-average gravel vacuum to reach the bottom without getting your shoulders wet!

Consistency is the secret to a crystal-clear tank. Because the water volume is relatively small, parameters can shift quickly if you skip your weekly chores. Stick to a routine, and your fish will thank you.

Weekly Maintenance Checklist

• Water Change: Perform a 20-25% water change weekly to remove nitrates and replenish minerals.
• Glass Cleaning: Use a magnetic scraper or a long-handled brush to clean all six panes of glass.
• Plant Pruning: Trim back fast-growers like Vallisneria so they don’t block too much light from the bottom.
• Filter Check: Rinse your filter sponge in old tank water (never tap water!) to keep the flow strong.

Managing Algae in Tall Tanks

Because the light has to be quite strong to reach the bottom, you might notice algae growing on the upper portions of your driftwood or the glass near the surface. This is perfectly normal in a deep tank.

To combat this, ensure you are not leaving your lights on for more than 8 hours a day. Adding fast-growing floating plants can also help by “shading” the tank and soaking up excess nutrients that would otherwise feed the algae.

Common Challenges and How to Solve Them

Every tank shape has its quirks. For the hexagon, the most common issue hobbyists face is “dead zones” where water doesn’t circulate. If you see debris piling up in a specific corner, your flow is likely blocked.

You can easily fix this by slightly adjusting the angle of your filter output. Even a small change can create a circular flow that sweeps the entire perimeter of the hexagon, keeping the water clear and the oxygen levels high.

Another common concern is finding a finding a secure cover. Because of the unique shape, standard rectangular lids won’t fit. Always ensure your hex tank has a tight-fitting lid, as many of the best fish for this setup (like Gouramis) are notorious jumpers!

Frequently Asked Questions

Can I keep Goldfish in a 20 gallon hexagon aquarium?

I generally do not recommend Goldfish for this tank shape. Goldfish require a lot of horizontal swimming space and produce a massive amount of waste. A 20-gallon hex is much better suited for small tropical community fish or shrimp.

Is a hexagon tank harder to clean than a rectangle?

It can be slightly more challenging because of the depth and the additional corners. However, with the right tools—like a long-reach algae scraper and a 24-inch gravel vac—it only takes a few extra minutes each week.

How many fish can I realistically fit?

In a 20 gallon hexagon aquarium, less is often more. Because of the limited surface area, you should stock more lightly than you would in a 20-gallon long. Aim for a “quality over quantity” approach with a few striking species.

Do I need CO2 for the plants?

For the plants mentioned in this guide (like Swords and Val), CO2 is not strictly necessary. However, using a liquid carbon supplement or root tabs will definitely help them thrive in the lower-light conditions at the bottom of the tank.

Final Thoughts for Success

The 20 gallon hexagon aquarium is a stunning piece of living art. By focusing on vertical aquascaping, ensuring high-quality filtration, and choosing fish that appreciate the height, you can create a thriving underwater sanctuary.

Remember to take things slow. Cycle your tank thoroughly before adding fish, and always keep an eye on your water parameters. With a little patience and the right equipment, your hexagon tank will be the envy of every guest who walks through your door.

Happy fish keeping! Whether you are a beginner or a seasoned pro, the vertical world of the hexagon tank offers endless opportunities for creativity and discovery. Dive in and enjoy the view!