There’s something about a 20-gallon cube that holds a special place in my heart. Maybe it’s because of the compact size, the perfect square dimensions which make them visually appealing, or the amount of versatility one gets out of it when aquascaping. Having worked on everything through the years, from small nano aquariums to larger ones like the 125-gallon behemoths, nothing does strike that balance quite as well as a 20-gallon cube. It’s small enough to be manageable and big enough to house an impressive aquascape.
I always find that the cube shape can support more creative layouts than the traditional rectangular tanks. Indeed, symmetry in the dimensions allows the tester to experiment with a variety of hardscape arrangements and provides excellent viewing angles from every side.
This would give the depth of the cube tank versus its width-a perfect dream for painting any aquascapist’s ultimate dream of scale and depth in the aquascape. It would be like working with a 3D canvas where you’re trying to paint not just width but also height and depth. One of my earlier projects working with a 20-gallon cube was a project I titled “Forest Retreat.” I remember looking at the blank canvas presented by the empty cube and immediately imagining a dense, mystical forest. I wanted it to bring the feel of a woodland clearing, with towering driftwood acting as trees, and lush carpeting plants filling the forest floor.
It wasn’t about placing plants and all types of rocks in order; the task was to compose an ecosystem that would appear to be alive. Later, the plants began to grow out, and moss-like wood started to look really aged. The view was such that every time I saw the tank, I felt like peeking in a tiny, forgotten corner of nature.
What I think I love most about these tanks, though, is how personal they become. A 20-gallon cube-a cube-is intimate, and you’re forced to make every inch of it count. There is no room for wasted space, uninspired design. Every detail, from how the rocks are stacked to the relationships created among the plants, needs to be well thought out. It’s a challenge, but it’s exactly what draws me in.
Section 2: Hardscaping-The Strong Foundation for Your 20-Gallon Cube It is in the hardscaping that any aquascaping design finds its backbone. Being a 20-gallon cube, this becomes all the more critical, providing a very vital basis needed by every other aspect: plant growth and water circulation alike. I am firm in my belief that the layout of rocks and driftwood can make or break an aquascape, and for that reason, I have spent countless hours tinkering with the sort of hardscape to be used. For me, the key to a strong hardscape is striking that balance between structure and fluidity. You want your rocks and wood to feel solid, as if they have been in place forever, yet dynamic in moving the viewer’s eye through the scene.
One technique that I think I’ll always recommend involves either the “Golden Ratio” or the “Rule of Thirds” in placing major features. This is one of the many naturally occurring aesthetic principles that act as a guide for keeping your layout within the bounds of the human eye.
This is even more important in cube tanks, because the viewer actually can see into the tank from different angles, and the layout needs to look balanced irrespective of where one stands.
Currently, one of the most memorable, if not favorite, hardscaping projects for me in a 20-gallon cube involves using Seiryu stone to give that jagged texture with a bluish tint that created an amazing contrast against plants of vibrant green color. I moved those rocks around for hours seeking a natural flow, like some mountain river cutting its path through chasm and gorge. That is another thing I have learned: just be in no great hurry to finish the hardscape. Step back often, view the tank from different angles, and even sleep on your design. Sometimes what seemed like just the right layout at night looks off the next morning.
One of the cool things with working with a cube tank is the extra depth you get from it when compared to the usual rectangular tank. You can play with layering-really place big stones up front and smaller ones toward the back, creating perspective and giving the feeling of more depth in your aquascape than is really there. When you add driftwood into this mix, it takes on an almost magical proportion. Spider wood created twisted, gnarly branches reaching up toward the surface in one of my more recent cube scapes, like some ancient tree’s roots. With some moss and ferns clinging to the branches, it became a focal point that really drew the eye in.
Of course, hardscaping isn’t all about aesthetics; it really needs to be functional, too. One mistake I perceive people making is not considering the water flow within a tank. Rocks and driftwood impact upon the water circulation, creating ‘dead zones’ where detritus can gather, or where the plants just won’t do as well. On my cube tanks, I have always tried to leave enough open space for the water to move around in. Remember, a good rule of thumb is checking how your filter and pumps move the water and adjust the hardscape accordingly.
Another important aspect of hardscaping is making sure the layout is stable. I have been guilty in the past of stacking rocks in a way that made them too precarious, shifting or falling when I began to fill the tank.
There is nothing worse than completing a nice aquascape and having it tumble at the first addition of water inside! Nowadays, I reinforce larger rocks and driftwood with aquarium-safe glue or zip ties, especially if they rest at odd angles. It’s a small step, but it makes a world of difference in the long-term stability of the aquascape. One thing that I always try to drive home while teaching beginners is that, when it comes to hardscaping, less is often more. It’s very tempting to try and cram as much rock and wood into the tank as possible, but personally I find minimalism can have a far greater effect.
I once did a cube “nature” aquarium with a few pieces of driftwood and two large stones, arranged in a manner that imitated that natural flow of a riverbed.
The elements were open to each other, allowing plants and fish to move in their natural way, creating a very serene open scene that was pleasing to look at.
More on substrate, I use a mix of fine gravels and aquasoil in my 20-gallon cubes. Aquasoil supplies at least most of the nutrients plants will need, while gravel serves both textural and stabilizing purposes.
I like sloping the substrate from front to back. That increases the sense of depth and makes the aquascape more immersive. This will also give me the opportunity to create little pockets with which I’ll be able to plant different species for a layering, more natural look. I can’t emphasize enough how rewarding it is to get your hardscape just right. It’s not merely about the planting of rocks and woods; it’s really about setting a framework upon which everything afterwards is built. When the hard-scaping is right, it’s as if everything else falls into place: plants grow much more naturally, fish interact with their environment in interesting ways, the whole aquascape ties in together.
Section 3: Selection and Care of Suitable Plants for 20 Gallon Cube Aquascape
Once the hardscape is done, the next phase in creating a 20-gallon cube aquascape is plant selection. I’ve often heard many say that picking out plants is the easy part of the aquascaping process, but as any seasoned aquascaper will be quick to point out, it’s rather more nuanced. It’s about choosing species that look good and thrive well in the environment one has created. Plant selection for a 20-gallon cube involves searching for a balance between aesthetics, growth habits, and maintenance considerations-you wouldn’t want the tank to be overwhelmed by fast growers that would need trimming weekly, nor those going to remain too small and get lost among your layout.
Among my first thoughts when handpicking plants for a 20-gallon cube involve determining the theme of the aquascape. Will it be more of a thick jungle-it would be dense, with tall-growing plants-or minimalistic, using a few strategically placed, slower-growing species? For example, in my “Forest Retreat” aquascape, I selected carpeting plants like Hemianthus callitrichoides, or dwarf baby tears, with midground plants such as Cryptocoryne wendtii to achieve the effect of a ‘forest’ bottom. I highlighted the scene with taller species like Bucephalandra and Rotala rotundifolia on the wood to give the impression of trees reaching upwards toward the canopy. Carpeting plants are a great way to maximally utilize space in a cube tank while giving it a green, cohesive look for a cube tank.
I personally like using Monte Carlo for this purpose. I love how it grows well in a 20-gallon cube and spreads fast across the substrate to create a thick, green carpet. Not quite as finicky as dwarf baby tears, Monte Carlo can be a bit more forgiving for those who do not have much experience with high-lighted and CO2-demanding plants. I remember my first attempt at growing a Monte Carlo carpet and how satisfying that was to gradually see it spread over the substrate.
Every week, plantlets come closer together; within months, the tank floor became covered with a thick green carpet. Indeed, it turned the tank into a mini-world.
Speaking of background plants, I tend to favor those species that tend to grow upwards but not “take over” the tank. Plants like Rotala and Pogostemon erectus work perfectly in a cube, adding height but without needing to be trimmed all the time. This would make both plants grow tall and complement the square of the tank, enhancing the sense of depth and verticality in the aquascape. I’ve found that using plants with different textures—like the fine, needle-like leaves of Pogostemon erectus alongside the broader leaves of Cryptocoryne—creates contrast that makes the aquascape visually interesting.
However, one of the challenges with keeping a 20-gallon cube is striking the right balance between plant growth and maintaining your tank. The thing about it is, because this tank is small, even a few fast-growing plants may quickly hog your tank, turning your well-thought-out aquascape into an unruly jungle.
I’ve made this mistake in the past, particularly with stem plants like Rotala and Ludwigia. While they grow beautifully, they can quickly outpace everything else in the tank, requiring frequent trimming to keep them from blocking light or choking out other species.
For this, I have learned to be selective with my planting density. This makes this process require much less maintenance compared with immediately stocking a full tank. The aquascape will mature naturally, and this can only be achieved with the passage of time. In fact, among my favorite aspects of aquascaping in a 20-gallon cube is watching it as plants would gradually fill in the nooks and gaps of the hardscape to eventually look full and natural.
I had thrown just a few stems of Rotala in the back of one of my tanks, and in several months, it filled in to become a nice, thick, bushy background that framed the rest of the aquascape quite nicely.
The other important aspect that drives the selection of the plants is the suitability of them with the lighting and CO2 conditions of your tank.
I usually adopt a medium to high lighting setup for my 20-gallon cube, mainly because this opens up more variety when it comes to plant species, which can be used in an aquascape, from carpeting plants to the more demanding stems. You don’t necessarily need high-tech setups with CO2 injection to create a beautiful aquascape, though. For example, I have a low-tech cube tank that contains the following plants: Anubias, Java fern, and Cryptocoryne, which in general are slow growers and don’t require CO2. These will also grow well in moderate light, and with proper care can make a beautiful, less-demanding aquascape that doesn’t need constant attention.
Speaking of CO2, I am a big believer in the use of CO2 on cube aquascapes, mainly when one aims for a dense growth of plants or carpeting species. For me, the addition of a good CO2 system has always made the difference between an aquascape that is healthy and vibrantly colored from other setups that struggle with algae and poor plant growth. I remember the first CO2 system set up on a 20-gallon cube-like it was a game changer. Plants perked up in days, colors were much more vibrant, and growth rates went through the roof. But with great power of CO2 comes great responsibility in careful monitoring; fluctuation can cause algae blooms or plant melt.
Speaking of algae, it is a concern in small tanks such as a 20-gallon cube. The key to keeping algae under control is a good balance between light, nutrients, and CO2. Throughout the years, I had my share of battles against both green spot algae and hair algae ; however, I have introduced one technique into my tanks, which adds some algae-eating species such as Amano shrimp or Otocinclus. They would help to keep the algae in check and, as a plus, add an extra layer of activity and life to the aquascape. Fish and invertebrates will round out the ecosystem in this 20-gallon cube, rather than being added strictly for algae-control purposes.
In cube tanks, I tend to stick with small schooling fish like the Ember tetras or Neon tetras-not too overwhelming. I also really enjoy working Betta fish into cube tanks, particularly when complemented by a planted aquascape. Their bright colors and flowing movements provide a nice contrast against green plants and hardscape. In conclusion, the 20-gallon cube aquascape represents a project with its unique features and requirements. Every element of this aquascape, from hardscape to plants, should work in harmony to reach balance in an inland ecosystem. I find that creating and maintaining a cube aquascape is just as fulfilling as the end product.
Founded adequately, a 20-gallon cube can be transformed into an exciting underwater landscape-a piece of nature in your home.
