How to Make a Terrarium in a Fish Tank [Aquarium Sea-Crets]

When it comes to containers commonly found in the home, fish tanks make an ideal terrarium candidate.

Large, evenly shaped, and endlessly versatile – what’s not to love?

And let’s be honest, most of us end up having one of these old fish tanks lying around somewhere. Plant terrariums need a lot less maintenance than fish aquariums so we might as well put them to use!

In reality, a fish tank can be used to create any type of terrarium, as long as you’re prepared to do a little (or sometimes a lot) of tinkering.

So in this ‘oh-fish-ial’ guide, we’re going to run through the main fish tank terrarium options and how to create them.

Off we go.

fish tank terrarium

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Fish Tank Terrarium Ideas and Key Options

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 the aquarium terrarium combination that is a paludarium. Waterfalls, shorelines, ponds – all are possible here.

In the next section, we’ll cover the conversion to a tropical terrarium, which can still form the basis of the more challenging builds too.

Let’s begin.

Aquarium to Terrarium Conversion [Step-by-Step]

1 | Select Your Aquarium Container

Aquariums come in all sizes and a variety of shapes/depths.

In all honesty, they’ll all work for your standard terrarium build. Starting from the small 10-gallon aquariums right up to the giant 50-gallon custom tanks.

Though if you’re taking in on to the vivarium or paludarium level, there will inevitably be a minimum size requirement as they’ll need to house extra equipment.

The next thing to consider is, 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.

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.

That’s what my friend Calum did.

fish tank terrarium
Here’s a (surprisingly thick) partial glass lid to allow for some airfow.

2 | Add/Create Your Background (If Desired)

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

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 background for your scene, or you can even slot in a ready-made one with minimal effort.

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.

fish tank terrarium
Alternatively, you can stick cork bark chips to a backboard like this one.

You can buy custom backgrounds already from the likes of Custom Reptile Habitats or just off Amazon.

A 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.

3 | Create Your Drainage Layer

Realistically, this is required of any of the above ideas. 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 waterlog-free!

I like to use LECA as my drainage material. 

leca terrarium
Leca works well in terrariums of all sizes.

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 is that 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. 

I always recommend a variation of the classic ABG mix.

A coco coir base, with orchid bark and sphagnum moss, plus earthworm castings for some organic fertilizer. Charcoal is a part of the classic mix, but I see it as an optional nice-to-have.

tropcial terrarium substrate
Tropical substrate mixes are always better than simple potting soil.

It doesn’t have to be this exactly, but it’s important to achieve the right qualities of water retention and drainage

Overall, ABG mix is a great balance of water retention and drainage, and tropical plants of all kinds just thrive in it. 

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.

fish tank terrarium
Look at the size of this suspended branch, and the size of the moss growing on it!

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

Personal favorites of mine are Mopani Wood and Dragon Stone but there are lots to choose from.

6 | Add Your Fish Tank Terrarium Plants

As a tropical terrarium with an (at least partially) sealed container,  you’ll want to choose from the selection of closed terrarium plants.

Those 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.

If you’re adding hardscape and/or a background (and I hope you do!) then add some epiphytes into the mix to really bring the space to life. Air plants, Bromeliads, and orchids are all fantastic options.

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 with sufficient coverage and intensity.

Sorry!

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.

fish tank terrarium
My friend ran with a Fluval light and has had incredible growth from it.

Now It’s Your Turn

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

Let me know how you got on in the comments! 

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