Fish Tank Terrarium: How to Turn an Aquarium Into a Terrarium

Fish tanks make brilliant terrariums.

Yes, you can use an old aquarium as a terrarium – and honestly, it’s one of the best containers for the job.

They’re wide, sturdy, and large enough to build something that looks more like a proper planted landscape. You get room for real layers, bigger pieces of hardscape, and a much more comfortable planting experience. Luxury, frankly.

So if you’ve got an empty fish tank sitting around, this is a very good second life for it.

In this guide, we’ll walk through how to turn a fish tank into a planted tropical terrarium, including setup options, layers, lighting, lids, plant choices, and fish tank terrarium ideas that actually work.

Turning a fish tank into a terrarium is a pretty straightforward process.

But they really shine when you lean into what the containers already do well. They’re literally designed for viewing, so you’re starting with a container that already gives you a clean, front-facing scene and plenty of room to work. Handy, that.

For this build, we’ll focus on a tropical planted fish tank terrarium – the lush, humid kind with moss, ferns, vines, wood, and a (mostly) covered lid.

1. Choose Your Fish Tank Container

Most aquarium tanks can work as terrariums.

Starting from the small 10-gallon aquariums right up to the giant 50-gallon custom tanks.

The next thing to consider – does it have a lid?

Not every fish tank comes with a lid, and those that do often only have partial coverage. If you’re opting for a typical tropical terrarium, you’ll need a lid with either full (or mostly full) coverage in order to trap humidity.

If your chosen fish tank doesn’t have a lid, don’t sweat it. It’s easy enough to get a custom acrylic (or even glass lid) cut to size for you. And if your lid does have gaps, it just means you’ll have to mist it more.

2. Add/Create Your Background (If Desired)

The size of the opening in a fish tank is one of its biggest assets.

It means you can easily get both your hands and your materials inside. This is why it’s a great opportunity to build a custom DIY terrarium background for your scene, or you can even slot in a ready-made one with minimal effort.

A terrarium background is entirely optional, but it can really pull a scene together and has the added benefit of creating 3D planting opportunities to mount vines and epiphytes.

If you’re going the DIY route, you can use expanding foam to create the structure and then apply your substrate (stuck with silicone as glue) to give it a natural-looking finish.

3. Create Your Drainage Layer

A drainage layer is highly recommended for any fish tank terrarium due to the amount of watering they tend to require.

Especially if you’re adding a heavy-duty misting system that’s going to periodically soak the whole thing.

Adding a drainage layer (otherwise known as a false bottom) provides a reservoir for excess water to collect once the substrate is saturated. Helping to keep your plants happy, healthy, and waterlogged-free!

I like to use LECA clay balls as my drainage material.

Though any tough, granular material will work, in larger fish tanks, weight can become an issue. So lightweight clay pebbles are preferable to heavy gravel or river rocks.

Plus, unlike delicate bottles and jars, with a sturdy fish tank, you can feasibly craft a legitimate drainage mechanism into the build, i.e., you can drill a drainage hole or valve into it if you like.

4. Add Your Substrate 

Step away from the potting soil…

A high-quality tropical mix is what will help keep your plants happy and those all-important humidity levels high. 

Alternatively, a variation of the classic ABG substrate is always a good shout.

Our signature terrarium soil mix is inspired by the classic ABG mix. Consisting of a coco coir base with orchid bark, charcoal, and earthworm castings for some organic fertilizer.

Terrarium Substrate Mix (Premium Blend)

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Fish tanks give you enough room to add a proper substrate layer, so use that space. Aim for at least 3+ inches, and slope it higher toward the back to create depth.

That slope makes a huge difference visually. A flat layer of soil across a rectangular tank can make even nice plants look oddly staged.

5. Bring in Your Chosen Hardscape

Here, we’re talking about your driftwood branches and your rocks. 

These larger materials will shape the structure of your terrarium scene, so it’s worth putting them in early so you know what space you have to work with.

Hardscape is arguably optional, but I believe it’s essential in creating an interesting and natural environment. This is especially true for larger terrariums like fish tanks, which really need a conscious design to create focal points to draw the eye.

Otherwise, you end up with a flat-looking scene with isolated plants.

Start with the largest piece first, then build around it.

6. Add Your Fish Tank Terrarium Plants

As a tropical terrarium with an (at least partially) sealed container, you’ll want to choose plants that are going to thrive in high moisture and humidity.

Honestly, any tropical terrarium plant is going to thrive in a fish tank terrarium, but it does present a unique opportunity to use larger plants and more aggressive vines (no pressure, just saying).

To get the most from your large tank space, you’re going to want a nice variety of species – in size, texture, and growth habits.

That’s the best way to get a dynamic and natural-looking scene.

I’d recommend a hearty mix of:

• Ferns – No tropical terrarium would be complete without one, and they bring so much texture to the table.
• Vines – Ground cover vines will help to create a natural undergrowth, and climbing vines bring that element of wild growth.
• Foliage – You’ll need a handful of bright, colorful, or outright weird plants to draw the eye and highlight certain sections.
• Moss – The verdant green glue that binds a terrarium together.

Live Cushion Moss

The classic terrarium moss. Lush, bouncy, and verdant green – perfect for adding instant softness and contrast.

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If you’re adding hardscape and/or background (and I hope you do!), then add some epiphytes into the mix to really bring the space to life.

7. Choose Your Lighting Solution

Artificial lighting isn’t strictly necessary if you have a good natural lighting spot for your terrarium.

However, with the size and depth of a typical fish tank terrarium, you’re unlikely to find one that works.

Aquariums are naturally wide and deep, so a nearby window often gives uneven coverage. One side tends to grow beautifully, and the other side slowly gives up. Not ideal.

To be honest, where possible, I’d recommend artificial lighting for any terrarium setup as it’s a whole lot easier than managing changing natural light. Fish tanks have a whole host of lighting options geared for them already, so it’s definitely worth it.

Grab yourself an aquarium strip light that fits across the top, and you’re set.

When it comes to utilizing a fish tank for a terrarium, there’s a wide range of ways to play it.

From a hi-tech conversion to fancy waterfalls and misting systems, right down to a simple low-tech houseplant garden – the possibilities are endless.

Here are some ideas in a loose order of increasing fun difficulty.

1 | Houseplant Planter – The simplest of all, simply pop in your potted houseplants so that they can enjoy the extra humidity of an enclosed terrarium. You can still strategically place elements like rocks and driftwood branches to hide the pots and create a more natural appearance.

2 | Desert Terrarium – You’ll need to keep the lid off for this one (as arid plants can’t handle the humidity), but a fish tank can be sculpted into a wonderful cacti and/or succulent terrarium. Succulents can still enjoy the extra space and will really appreciate the addition of a UV strip light.

3 | Tropical Terrarium – The volume and accessibility of a fish tank is an amazing blank canvas for a tropical terrarium. This will be the focus of the step-by-step guide coming up in the next section, so stay tuned!

4 | Vivarium – Creating an environment for an animal definitely ups the ante somewhat. That said, with the addition of a few extra bits of equipment, a suitably sized fish tank can become a home for all sorts of critters.

5 | Paludarium – Naturally, a container originally designed to house an underwater world lends itself well to a paludarium setup (aquarium/terrarium combination). Waterfalls, shorelines, ponds – all are possible here.

There you have it, the ‘fin-ale’ of our guide to how to make a fish tank terrarium.

You’d think there are some niche skills involved in converting an aquarium, but it’s actually one of the easiest possible builds. We had a lot of fun building this example, and we’ve used tanks again and again.

So if you’ve got an old aquarium sitting empty, this is your sign to clean it out and turn it into something green again!

Let me know how your fish tank terrarium turns out in the comments.

And if you need some more inspiration for your next project, check out our post on the best terrarium ideas (that actually work).