How To Turn A Fish Tank Into A Terrarium – The Ultimate Guide

Do you have an old 10-gallon or 20-gallon aquarium gathering dust in your garage or basement? You aren’t alone; many of us in the hobby eventually upgrade to larger setups, leaving our starter tanks behind.

If you’ve been wondering how to turn a fish tank into a terrarium, you are about to embark on a rewarding DIY journey. Repurposing a glass tank into a lush, green indoor garden is one of the most satisfying ways to bring nature into your home.

Whether you want to grow exotic tropical plants or create a miniature desert landscape, your old aquarium is the perfect vessel. Don’t worry—this setup is perfect for beginners and seasoned aquarists alike!

In this comprehensive guide, we will walk through every step, from choosing the right materials to maintaining a thriving ecosystem. Let’s dive in and breathe new life into that old glass box.

Why Repurpose Your Fish Tank into a Terrarium?

Before we get our hands dirty, it’s worth discussing why a fish tank is actually superior to many traditional terrarium containers. Fish tanks are designed to be water-tight and durable, which is a massive advantage.

Standard aquariums are made of high-quality glass or acrylic that offers crystal-clear visibility. This makes them ideal for showcasing intricate mosses and delicate foliage that might be lost in a ceramic pot.

Furthermore, the rectangular shape of most fish tanks provides a significant “footprint.” This allows you to create depth and perspective in your landscaping that round jars simply cannot match.

Materials You Will Need for the Conversion

To succeed, you need to think beyond just “dirt in a box.” A functional terrarium requires a specific layering system to prevent root rot and manage moisture effectively.

Here is a checklist of the essential supplies you should gather:

• An old fish tank: Cleaned and dried thoroughly.
• Drainage layer: LECA (lightweight expanded clay aggregates), lava rock, or pea gravel.
• Substrate barrier: A fine mesh or window screen cut to the size of your tank.
• Activated charcoal: To keep the system fresh and prevent odors.
• Terrarium substrate: A mix of coco coir, orchid bark, and sphagnum moss.
• Plants: Tropical species for closed tanks or succulents for open tanks.
• Hardscape: Decorative rocks, driftwood, or cork bark.
• Tools: Long tweezers, a spray bottle, and a small shovel.

Step-By-Step Guide: how to turn a fish tank into a terrarium

Now that you have your supplies, it is time to start the build. Follow these steps carefully to ensure your new ecosystem remains healthy and vibrant for years to come.

1. Cleaning and Preparation

The first step is crucial. You must ensure the tank is free from old algae, calcium deposits, or chemical residues. Use a vinegar-and-water solution to scrub the glass.

Avoid using harsh soaps or detergents, as these can leave residues that are toxic to sensitive plants. Once cleaned, dry the glass thoroughly with a microfiber cloth to prevent water spots.

2. Creating the False Bottom

Because a fish tank does not have drainage holes, you must create a false bottom. This is where excess water will sit, keeping it away from your plant roots.

Pour about 1 to 2 inches of LECA or lava rock into the bottom of the tank. This layer acts as a reservoir, ensuring your plants don’t succumb to “wet feet” and rot.

3. Installing the Barrier and Charcoal

Place your mesh screen directly on top of the drainage layer. This prevents the soil from falling into the rocks and clogging the drainage system.

On top of the mesh, sprinkle a thin layer of activated charcoal. This is the “secret sauce” of a healthy terrarium, as it filters impurities and prevents the growth of mold.

4. Adding the Substrate Mix

Now, add your substrate. For a tropical setup, a mix often called the “ABG mix” (Atlanta Botanical Gardens) is the gold standard. It provides excellent aeration and moisture retention.

Aim for a substrate depth of at least 2 to 3 inches. You can even slope the soil towards the back of the tank to create a sense of scale and depth.

5. Hardscaping Your Landscape

Before planting, place your larger decorative elements like rocks or driftwood. Think of this as the “skeleton” of your terrarium.

Positioning a large piece of Manzanita wood or a few pieces of Dragon Stone can create a focal point. This step is where you can truly express your creativity as an aquarist.

Choosing the Right Plants for Your Setup

The plants you choose will depend entirely on whether you plan to keep the tank open or covered. Most fish tanks come with a lid, making them ideal for tropical, high-humidity environments.

Tropical Plants (Closed or Semi-Closed Tank)

If you keep the lid on, you are creating a “closed” system. These plants thrive in consistently moist soil and high humidity levels.

• Fittonia (Nerve Plant): Famous for their bright pink or white veins.
• Ferns: Lemon Button or Maidenhair ferns add wonderful texture.
• Mosses: Java moss (yes, the aquarium kind!) or Cushion moss work beautifully.
• Pilea: Also known as the Aluminum plant, these are very hardy.

Succulents and Cacti (Open Tank)

If you prefer an open-top look, you should opt for plants that enjoy dry air and bright light. However, be careful with watering since there are no drainage holes.

• Haworthia: These are slow-growing and very resilient.
• Echeveria: Beautiful rosette shapes that come in many colors.
• Air Plants (Tillandsia): These don’t even need soil; you can nestle them in the hardscape.

Lighting Requirements for Your New Terrarium

One of the best things about learning how to turn a fish tank into a terrarium is that you can often use your existing aquarium light. However, there are a few things to keep in mind.

Standard aquarium LED lights are usually sufficient for low-to-medium light plants like ferns and mosses. If you are growing high-light succulents, you may need a full-spectrum grow light.

Avoid placing your glass tank in direct sunlight. The glass can act like a magnifying glass, rapidly heating the interior and scorching your plants. Indirect, bright light is always the safest bet.

Managing Humidity and Ventilation

In a converted fish tank, air circulation is often the biggest challenge. Unlike professional terrariums, aquariums are designed to keep things in, not let air flow through.

If you notice excessive fogging on the glass, your terrarium might be too wet. Simply leave the lid open for a few hours a day to allow for fresh air exchange.

For a closed setup, you want a light misting on the glass in the morning that clears up by the afternoon. This indicates a perfectly balanced water cycle.

Maintenance and Long-Term Care

Once established, a terrarium is remarkably low-maintenance. However, it still requires a watchful eye to ensure it stays healthy.

Watering: Only water when the soil feels dry to the touch or if the moss looks slightly crispy. Use a spray bottle to mist the plants rather than pouring water in.

Pruning: In a confined space, plants will eventually outgrow their home. Use sharp, sterilized scissors to trim back any foliage that is touching the glass or crowding out other plants.

Cleaning: Over time, the glass may get dusty or develop a bit of algae. Use a damp paper towel to wipe the inside of the glass. Never use glass cleaner inside the tank!

Troubleshooting Common Issues

Even experts face challenges when learning how to turn a fish tank into a terrarium. Here are a few common problems and how to solve them:

1. Mold Growth

If you see white, fuzzy mold, it usually means there is too much moisture and not enough airflow. Remove the mold manually and leave the lid off for a day.

2. Yellowing Leaves

Yellow leaves are often a sign of overwatering. Check the drainage layer; if there is a lot of standing water, you may need to use a turkey baster to siphon it out.

3. Leggy Plants

If your plants are growing tall and thin with lots of space between leaves, they are “reaching” for light. Move your light source closer or increase the duration of the lighting cycle.

Enhancing Your Terrarium with Microfauna

To create a truly self-sustaining ecosystem, consider adding “Clean-Up Crew” organisms. These tiny creatures help break down decaying matter and prevent mold.

• Springtails: These tiny white insects are the powerhouse of any terrarium. They eat mold and fungi.
• Isopods: Also known as pill bugs, they help cycle nutrients back into the soil.

Adding these will make your terrarium much more biologically stable and mimic a real-world forest floor. It’s a fascinating addition that many aquarium hobbyists find very familiar!

Frequently Asked Questions (FAQ)

Can I use any fish tank for a terrarium?

Yes! Any glass or acrylic aquarium can be used. However, taller tanks are better for climbing plants, while long tanks are better for creating expansive landscapes.

Do I need a lid for my terrarium?

It depends on your plants. Tropical plants love the humidity of a lid, while succulents prefer the dry airflow of an open tank.

How often should I water my converted fish tank terrarium?

For a closed tank, you may only need to water once every 2-4 months. For an open tank, check the soil weekly and water sparingly.

Can I keep animals in my new terrarium?

If you want to keep frogs or reptiles, you must ensure the tank is properly ventilated and heated. A simple plant terrarium is much easier to maintain than a vivarium with livestock.

Is activated charcoal really necessary?

While not strictly required, it is highly recommended. It acts as a biological filter, keeping the air and soil smelling fresh by trapping toxins.

Conclusion

Learning how to turn a fish tank into a terrarium is a fantastic way to extend the life of your aquarium equipment. It allows you to explore a different side of the “glass box” hobby without the need for water changes or nitrogen cycles.

By following the layering process—drainage, barrier, charcoal, and substrate—you create a foundation for success. Whether you build a tiny mossy forest or a rugged desert scape, your new terrarium will be a stunning focal point in your home.

So, go grab that old tank from the garage, pick out some beautiful tropical greens, and start planting. You’ll find that gardening under glass is just as addictive and rewarding as keeping fish!

Happy planting, and welcome to the wonderful world of indoor glass gardening!