I wasn’t supposed to buy another tank. I’d promised my partner after the “great tank explosion of 2019” (don’t ask) that I was at capacity. No more glass boxes of water in our already cramped apartment.
But then I saw it – a perfect 20cm cube, crystal clear glass with nearly invisible seams, sitting on a clearance shelf at my local fish store. Eight dollars. EIGHT.
How was I supposed to resist that? It was practically a moral obligation to rescue it. “It’s tiny,” I explained later, as if its diminutive size somehow exempted it from our moratorium on new tank setups.
“It’s basically a vase.” This argument was not as persuasive as I’d hoped, but the tank was already home, and my mind was racing with possibilities. Working with a 20cm nano tank is completely different from anything larger – it’s bonsai underwater gardening, where every millimeter matters and small mistakes become glaring failures. My first attempt was predictably disastrous.
I approached it like a miniaturized version of my larger tanks, which was fundamentally wrong. I used standard aquasoil, regular-sized hardscape, and plants that would eventually outgrow the space. The result looked like a cluttered underwater junk drawer rather than the serene minimalist scene I’d envisioned.
Lesson one: nano tanks require specialized thinking, not just scaled-down standard approaches. Let’s talk about what actually works in a 20cm nano tank, based on my many failures and occasional successes. First, hardware.
Standard equipment is your enemy here. That filter designed for “tanks up to 10 gallons”? It will create a whirlpool effect in your tiny cube.
That normal-sized heater? It will dominate the visual space. You need to think different.
For filtration, I’ve had the most success with tiny sponge filters powered by air pumps that can be hidden behind hardscape. Even then, I use flow control valves to reduce the bubbling to a gentle trickle. My current 20cm setup uses a small USB-powered air pump that makes less noise than my laptop fan.
Alternatively, some nano-specific internal filters work well if you design your hardscape to conceal them. Heating is tricky. Many nano tanks exist in living spaces that maintain relatively stable temperatures, and honestly, if your home stays between 72-78°F (22-26°C), you might be able to skip a heater altogether, especially if you’re keeping plants and shrimp rather than tropical fish.
If you do need heating, look for the flat heating mats designed to go under nano tanks, or the new generation of tiny in-line heaters that can be hidden in your filter system. Lighting for a 20cm cube should be small but mighty. I’ve tried multiple options, from expensive aquascaping-specific lights to modified desk lamps.
My current favorite is actually a small clip-on LED intended for indoor houseplants, modified with a simple timer. It provides surprisingly good PAR values and cost less than $20. Whatever you choose, make sure it’s dimmable – the line between “adequate light for plant growth” and “perfect conditions for algae bloom” is razor-thin in nano tanks.
Now for the fun part – hardscape. This is where most 20cm tanks go wrong, including my early attempts. Standard aquascaping stones and driftwood pieces that look appropriate in larger tanks appear cartoonishly oversized in a 20cm cube.
I’ve had the most success using small fragments of larger hardscape materials – the broken bits that stores often sell at discount because they’re too small for standard tanks. For my most successful 20cm tank, I actually took a larger piece of spider wood and carefully broke it into fragments, then reassembled selected pieces using super glue gel (cyanoacrylate is aquarium safe once cured) to create a hardscape that looked naturally proportioned for the tiny space. For stones, I collected small pebbles from a landscaping supply yard, boiled them thoroughly, and arranged them to mimic the look of larger stone arrangements.
Substrate depth becomes critically important in nano tanks. That inch of substrate that looks perfectly reasonable in a standard tank will eat up a significant percentage of your water volume in a 20cm cube. I now use aquasoil or similar active substrates in a gradient – as thin as 1cm in the foreground ranging to 2-3cm in the back.
This creates natural-looking depth while maximizing water volume. The greatest challenge with 20cm nano tanks is avoiding the dreaded “dollhouse effect” – where everything looks like a too-perfect miniature rather than a convincing underwater scene. The key to overcoming this, I’ve found, is appropriate scale in every element.
This means tiny-leaved plants, very small hardscape elements, and fine-grained substrate. Plant selection is where many nano tanks succeed or fail. Those beautiful stem plants that grace the backgrounds of larger tanks?
They’ll outgrow your nano setup in weeks. That Amazon sword that looks so lush in the store? It will literally fill the entire tank within months.
For 20cm tanks, I focus almost exclusively on the smallest varieties available. My go-to plants for nano tanks include Anubias nana ‘petite’ (or even better, ‘micro’), Bucephalandra ‘wavy green mini’, Monte Carlo for carpeting (HC Cuba works too but requires more maintenance), Cryptocoryne parva (the smallest crypt), and mosses like mini Christmas moss or Fissidens fontanus. For stem plants, if you must have them, Rotala ‘H’ra’ can work if aggressively trimmed, as can Micranthemum ‘Monte Carlo’ used as a stem plant rather than a carpet.
I still remember the day I discovered Utricularia graminifolia – a carnivorous aquatic plant with leaves so tiny they appear almost like a soft green cloud. It became the centerpiece of my most acclaimed nano tank, creating an otherworldly effect that was perfectly scaled to the 20cm format. Unfortunately, it’s also incredibly demanding to grow, requiring pristine water conditions and CO2 injection.
Nothing worthwhile comes easy in this hobby. Maintenance rhythm is everything with nano tanks. The smaller water volume means parameters can shift quickly, and problems compound rapidly.
I do 30-40% water changes twice weekly on my nano setups, using a designated turkey baster (yes, really) to remove water and a small plastic cup for refilling. The entire process takes less than five minutes but makes an enormous difference in stability. Fertilization requires extraordinary care in nano tanks.
I dilute all commercial fertilizers to 1/4 strength and dose with pipettes to ensure accuracy. Even then, I start with half the recommended frequency, watching plant response carefully before increasing. It’s much easier to add nutrients gradually than to fight the algae bloom that results from overdosing.
CO2 in 20cm tanks is a controversial topic among nano enthusiasts. Some swear by it, others avoid it entirely. I’ve tried both approaches and found that while CO2 does improve plant growth dramatically, it introduces another layer of complexity and risk in such small water volumes.
My current 20cm tank runs without pressurized CO2, using liquid carbon supplements instead. The growth is slower, but the maintenance burden is significantly lighter. The greatest joy of 20cm nano tanks, for me, is how they reward close observation.
These tiny underwater worlds don’t announce their beauty from across the room – they invite you to draw near, to spend time watching, to notice the minute changes that occur daily. My current desktop nano contains a small colony of cherry shrimp, and I’ve spent embarrassing amounts of time watching their tiny social interactions, molting rituals, and foraging behaviors. One particular female shrimp – recognizable by a distinctive white patch on her head – has produced three generations of offspring in this tiny ecosystem.
I’ve watched her berried with eggs, then carrying dozens of nearly invisible shrimplets under her tail, then releasing them to venture through the mosses and microplants. It’s a complete life cycle playing out in less space than a shoebox. If you’re considering a 20cm nano tank, approach it with patience and humility.
These tiny systems punish hubris and reward restraint. Start simple – a few small hardscape elements, two or three plant species at most, and maybe a small colony of shrimp. Let the system stabilize completely before even considering fish.
Accept that your first attempt might fail spectacularly. Mine certainly did. But there’s something uniquely satisfying about creating a complete, balanced ecosystem in such a small space.
When it works – when the plants pearl with oxygen, the water remains crystal clear, and tiny creatures thrive among the carefully arranged elements – it feels like you’ve captured a perfect moment of natural harmony in a glass cube. My 20cm nano tank sits on my desk, just at the edge of my peripheral vision while I work. Throughout the day, I catch glimpses of movement – tiny shrimp going about their business, plants swaying gently in the filter flow.
In moments of stress or creative blockage, I find myself drawn to it, watching the contained underwater world where life continues at its own perfect pace, unbothered by deadlines or expectations. There’s a peculiar peace in that, a reminder that sometimes the smallest spaces contain the most profound experiences.
