Why I’m Obsessed with 20cm Tanks (And You Should Be Too)

So I’ve been getting a lot of questions lately about my tiny cube tank setup on my kitchen counter – the 20cm one that fits perfectly next to my coffee maker. People see it in my Instagram stories and assume it’s just some starter tank I’m using before “upgrading” to something bigger. But honestly? This little 8-inch cube might be my favorite tank I’ve ever set up, and I’ve been doing this for years now.

Here’s the thing about really small tanks that nobody tells you – they’re not easier than big tanks. They’re actually way harder. But they’re also incredibly rewarding once you figure them out, and they’re perfect for people like me who live in apartments where every square inch matters. Plus, you can create something genuinely stunning without spending hundreds of dollars or taking over your entire living room.

I remember my first attempt at a nano cube like this. Total disaster. I had this vision of creating a perfect little Iwagumi layout – you know, those minimalist Japanese-style scapes with just rocks and carpet plants. Bought three tiny pieces of Seiryu stone from my local fish store (cost me like twelve bucks, which felt steep at the time), got some dwarf baby tears that were supposed to carpet the bottom. The guy at the store was like “good luck with that” which should have been my first warning sign.

Everything seemed fine for the first couple weeks. The plants were doing their thing, the rocks looked pretty decent arranged in my attempt at following the rule of thirds. Then my apartment’s heating system went wonky – dropped the temperature maybe three degrees for a few days. In a bigger tank, that’s nothing. In this tiny volume? Complete algae explosion. Green hair algae everywhere, my expensive little carpet plants just melted into brown mush. I was so frustrated I almost gave up on small tanks entirely.

But I’m stubborn, especially when I’ve already spent money on something. Started researching why small volumes are so unstable, learned about how every little change gets magnified when you’re dealing with just a few gallons of water. It’s like… imagine trying to balance on a tightrope versus walking on solid ground. Any tiny wobble becomes a major problem.

That’s when I really started appreciating the challenge. In my bigger 10-gallon, I can mess up water parameters slightly and nothing terrible happens. Plants keep growing, fish stay happy, life goes on. In a 20cm cube? Every decision matters. The placement of each rock, the type of plants you choose, how much light you give it, CO2 levels – everything has to be dialed in perfectly.

What I’ve learned over probably six or seven different iterations of this tank is that simplicity wins. Those dense jungle-style layouts that look amazing in big tanks? They’re overwhelming in a tiny space. The Iwagumi approach actually works perfectly at this scale – a few well-chosen stones, maybe some driftwood, and carefully selected plants that won’t take over.

My current setup uses three pieces of Ohko stone (dragon stone) that I got from a local aquascaping group buy – way cheaper than buying retail. The main stone is slightly off-center as a focal point, with two smaller pieces creating visual balance. I’ve carpeted most of the bottom with dwarf hair grass instead of baby tears because it’s more forgiving and doesn’t melt as easily when things get slightly out of whack.

Here’s something I wish I’d known earlier – hardscape selection is everything in small tanks. I made the mistake once of using stones that were too big, made the whole thing look cramped and fake. Then I overcorrected and used tiny pebbles that looked completely out of proportion. Finding that sweet spot where the rocks look natural but appropriately sized for the space took way more trial and error than I expected.

Spider wood is another material I love for nano tanks. It has this twisted, branchy look that adds organic movement to the layout. I’ve got a piece in my 3-gallon shrimp tank with flame moss growing on the branches – looks like tiny green fire reaching up toward the light. Cost me maybe eight dollars total and it’s been the centerpiece of that tank for over a year.

Plant selection is where I see most people mess up small tanks. You can’t just scale down what works in a big aquarium. Those beautiful stem plants that create amazing backgrounds in large tanks? They’ll outgrow a 20cm cube in weeks and turn it into an overgrown mess. I learned this the hard way when I tried cramming Rotala and Ludwigia into a nano tank. Within a month it looked like a jungle that needed machete access.

Now I stick to low-growing species that stay compact. Crypts are amazing for this – Crypt parva especially stays tiny and adds nice texture without taking over. Staurogyne repens is another favorite because you can trim it to keep it bushy and low. For carpeting, I’ve had way better luck with dwarf hair grass than baby tears, even though baby tears look more impressive when they work.

One thing that’s different about nano aquascaping is you have to think about negative space more carefully. In a big tank, you can fill areas with plants and still have room to breathe. In a 20cm cube, every planted area needs to be balanced with open space or it starts feeling claustrophobic. I actually keep notes now about plant placement because it’s so easy to overdo it.

Mosses are perfect for small tanks because you can use them creatively without adding bulk. Java moss, flame moss, Christmas moss – they all attach to hardscape and add softness without taking up substrate space. I’ve wrapped moss around driftwood branches to make them look more aged and natural. Takes months to really grow in, but the end result looks way more mature than a freshly planted tank.

Lighting is probably where I see the most problems with people starting nano tanks. It’s so easy to overlight a small volume and end up with algae disasters. I use a Chihiros A-series light on most of my small tanks, running it at maybe 60% intensity for six hours a day. More than that and I start seeing green spot algae or worse. Less and the plants don’t grow well. Finding that balance took months of adjusting.

Maintenance is where small tanks really show their personality. Water changes have to be more frequent but smaller volume. I do 15% twice a week instead of one big weekly change because sudden parameter swings are deadly in small volumes. I learned this after doing a large water change to combat some algae and shocking all my plants into melting. Not fun.

CO2 injection helps a lot with plant growth, but you have to be super careful not to overdo it. I use a small pressurized system with an inline diffuser – way better distribution than those cheap ceramic diffusers. The difference in plant growth was obvious within weeks of upgrading.

Filtration is tricky because most filters are overkill for such a small space. I use tiny sponge filters in most of my nano tanks. They provide gentle circulation without creating too much flow, plus they work as biological filters which is important in small volumes. Internal filters work too but they take up precious space inside the tank.

For livestock, less is definitely more. I tried putting six ember tetras in a 20cm cube once – seemed reasonable since they’re tiny fish. But even small fish produce waste, and the bioload was too much for the volume. Now I stick to just shrimp in most of my nano tanks. Cherry shrimp are perfect – they add color and movement, help clean up algae, and don’t add much bioload.

Nutrient dosing is another area where precision matters more in small tanks. I use liquid fertilizers designed for nano aquariums, dosing way less than the recommended amounts. It’s better to under-dose and gradually increase than to overdose and deal with algae outbreaks. I keep a dosing schedule taped to my fridge because consistency is key.

The cool thing about mastering a 20cm tank is that it makes you better at aquascaping in general. When every decision is magnified, you learn to be more intentional about plant placement, hardscape arrangement, and maintenance routines. The skills translate directly to larger tanks but with more margin for error.

What I love most about my nano tanks is how they fit into my lifestyle. They don’t dominate my apartment like a big tank would, but they still provide that connection to nature that drew me to this hobby. I can rearrange one completely in an afternoon, try new layouts without massive commitment, and still create something genuinely beautiful.

My current 20cm cube has been running for eight months now and it’s probably the most stable tank I’ve ever maintained. The carpet has filled in perfectly, the hardscape looks natural and mature, and my cherry shrimp are breeding like crazy. It sits right where I eat breakfast every morning and honestly makes starting the day better.

If you’re thinking about trying a nano tank, just know that it’s going to challenge you in ways bigger tanks don’t. But that’s exactly why they’re worth doing. When you finally get one dialed in perfectly, it’s this incredible little ecosystem that proves you don’t need massive space or budgets to create something amazing. Plus, they’re addictive – I started with one and now have three nano tanks scattered around my apartment. My boyfriend is surprisingly tolerant of this.