There’s something uniquely satisfying about working with a 20-liter tank. Not too small to feel cramped, not large enough to lose that intimate connection where you know every square inch intimately. It’s the Goldilocks zone of aquascaping – just right.
I’ve set up more 20L tanks than I can count over the years, each one teaching me something new about this peculiar art form that combines gardening, sculpture, and animal husbandry in a box of water. My first 20L was a complete disaster, as first attempts often are. I crammed it full of every plant that caught my eye at the local fish store – a rookie mistake I now watch countless beginners repeat.
“But they all looked so pretty!” Yeah, and they all have different requirements, growth patterns, and eventual sizes. Three weeks in, I had a tangled mess of melting Cryptocorynes (thanks to my incessant replanting), stem plants reaching desperately for the surface, and an Anubias slowly dying because I’d buried its rhizome in substrate. Live and learn.
The breakthrough came when I started thinking in terms of constraints rather than possibilities. Instead of asking “what can I add?” I began asking “what should I leave out?” This shift transformed my approach to the 20L format. I stopped seeing the limited space as a restriction and started viewing it as a creative challenge – how to create maximum impact with minimal elements?
Temperature management is trickier in a 20L than most people realize. The smaller water volume means fluctuations happen rapidly, especially if your tank sits near a window or an AC vent. I learned this lesson the expensive way after cooking a beautiful setup during a summer heat wave when my apartment’s AC failed.
I came home to find the tank at 93°F and most of my carefully cultivated Monte Carlo carpet floating at the surface, roots and all. Now I use a small, adjustable heater even in summer, set just a few degrees below room temperature as a safety measure against overheating. Lighting a 20L presents a specific challenge.
Most commercial lights are either too weak (leading to leggy, stretched plant growth) or too powerful (hello, algae farm!). After trying numerous options, I’ve settled on adjustable LED systems that allow me to dial in the exact intensity needed. Start lower than you think you need – around 50-60% intensity for 6-7 hours daily – and slowly increase based on plant response.
The best indicator isn’t algae presence (that’s already too late) but the compact, healthy growth of your plants. If stems are stretching with long internodes between leaves, you need more light. If existing leaves are developing spots or yellowing prematurely, you might have too much.
Filtration is where many 20L setups go wrong. Those tiny hang-on-back filters that come with kits? They’re rarely sufficient for a planted tank.
But powerful canister filters can create too much flow, turning your carefully positioned plants into underwater weathervanes permanently bent in the current. I’ve had the most success with small, adjustable canisters with spray bars that distribute flow evenly. And please, for the love of all things aquatic, use an intake sponge.
I still have nightmares about the time I found a cherry shrimp halfway through a filter intake tube, waving its tiny appendages at me like some kind of horrifying puppet show. The hardscape makes or breaks a 20L aquascape. With limited space, every stone and twig matters.
I typically spend hours – sometimes spread across days – arranging hardscape before adding a drop of water. My long-suffering partner has learned to recognize “the look” when I’m deep in hardscape arrangement mode and knows better than to ask questions like “haven’t you been moving the same rock for 45 minutes?” Yes. Yes I have.
Because that rock is the cornerstone of the entire design, and two millimeters to the left makes all the difference between “eh, nice tank” and “wow, how did you create such depth?”
My approach to hardscape in 20L tanks follows what I call the “rule of uneven thirds.” Instead of centering the focal point, I place it roughly 1/3 from either side (never dead center), and I use stones or wood of noticeably different sizes. Three stones? Make sure one is clearly larger, one medium, one smaller.
This creates natural visual hierarchy and avoids the dreaded “lineup” effect where everything seems artificially arranged. I learned this from years of frustration, wondering why my technically “correct” arrangements lacked the natural feel I was seeking. Substrate choice matters enormously in a tank this size.
That inch or inch-and-a-half layer represents a significant percentage of your total volume, so it needs to pull its weight functionally and aesthetically. For planted 20L tanks, I’ve had the best results with aquasoil-type substrates that provide nutrients while maintaining their shape over time. Sand looks gorgeous initially but can compact around plant roots, and plain gravel requires constant root tab fertilization.
That said, I do love using sand for paths or foreground accents in aquasoil-based tanks. There was the memorable disaster when I tried to create raised substrate areas without proper support structures. I spent hours carefully shaping hills and valleys, planted everything perfectly, filled the tank with exquisite care…and woke up the next morning to find everything flattened, plants uprooted, and the water so cloudy I couldn’t see the back glass.
Now I use small pieces of slate or plastic mesh to create terraces before adding substrate. Learn from my pain, friends. For plants, the 20L format rewards careful selection over quantity.
I’ve moved away from stem plants in most of my 20L designs, focusing instead on slow-growing epiphytes (Anubias nana ‘petite’ and Bucephalandra varieties are favorites), undemanding cryptocorynes, and carpeting plants like Monte Carlo or Marsilea hirsuta that stay naturally short. The goal is to create a setup that maintains its intended form without requiring weekly aggressive pruning. My fertilization approach for 20L tanks is lean by most standards.
I dose at roughly half the recommended rate for commercial liquid fertilizers, increasing gradually only if I see clear signs of deficiency. In a tank this size, it’s much easier to add more nutrients than to remove them once algae takes hold. This conservative approach has served me well, particularly in aquascapes where the hardscape is a significant element.
CO2 is not mandatory for 20L success, despite what Instagram might lead you to believe. I’ve created beautiful, healthy tanks both with and without CO2 injection. If you do go the CO2 route, invest in a proper regulator with a solenoid connected to your light timer.
The single worst tank crash I ever experienced came from a cheap CO2 system that dumped its entire contents into my 20L overnight. I still feel guilty about the mass extinction event I created through carelessness. Water change discipline is non-negotiable with 20L tanks.
Small water volumes mean parameters can shift quickly. My maintenance rhythm is simple: 30% weekly water changes, performed religiously. Not when algae appears, not when nitrates creep up, but every single week regardless of how pristine the tank looks.
This consistency prevents problems rather than addressing them after they’ve taken hold. For livestock, restraint is key. I know we all want to see movement and life in our carefully crafted underwater gardens, but overstocking is the fastest route to instability.
For a 20L, I recommend choosing either a small school (6-8) of nano fish like chili rasboras or green neon tetras, OR a centerpiece fish like a honey gourami or scarlet badis, OR a colony of dwarf shrimp. Not all three, not even two of the three – just one group, kept well. I made this mistake early on, convincing myself that because the fish were small, I could keep more of them.
The resulting ammonia spike taught me humility and cost me both fish lives and a carpet of HC Cuba I’d spent months nurturing. These days, I’d rather have a few fish in perfect health than a crowd under stress. I’ve come to appreciate the 20L format as the perfect training ground for larger aquascapes.
The principles remain the same, but mistakes are less costly and easier to correct. There’s also something deeply satisfying about creating a complete underwater world in such a modest space – a world that can sit on a desk or shelf, bringing life and movement to otherwise static rooms. My current favorite 20L sits on my office desk, a simple Iwagumi-inspired layout with three stones of decreasing size, a carpet of Monte Carlo, and a small group of celestial pearl danios that shimmer like living jewels when they catch the light.
It’s not the most complex tank I’ve created, not the most technically impressive. But it’s in perfect balance, requiring minimal maintenance while providing maximum joy. And really, isn’t that what this hobby is all about?
If you’re considering trying your hand at a 20L aquascape, approach it with patience and intention. Plan meticulously, execute carefully, and be willing to adapt when things don’t go as expected (and they won’t). The journey will teach you as much about yourself as it does about aquascaping – about your relationship with control, your capacity for observation, and your willingness to partner with rather than dominate natural processes.
Few hobbies offer such profound lessons in such a small package.
