Small thinking for big aquariums...

You hear me talk about this idea all the time...keeping small fish in large aquariums. Now, this is not some kind of unique, revolutionary position in the aquarium hobby. However, I think it's something we take for granted at the least, or simply assume is  more-or-less common practice.

It isn't, IMHO.

I was inspired to write this piece by a video I watched not too long ago on YouTube, where the talented fish geek/You Tuber set up a bunch of tanks- many of them  larger, and stocked with...lots of big 'ol fishes. He was talking about all of the emails he was receiving from fans who wanted to see him keep this-or-that "monster fish" in a specific large tank...I suppose a lot of people call this "aspirational", and who am I to question peoples' tastes?

I'm the guy who likes brown water, decomposing leaves, and biofilms, right?

Well, I will be honest. I found it a bit...(ouch) cliched...

Cue hateful emails.

I really couldn't think of another word for it. I mean, this was  so...expected.

And don't get it twisted.  I'm not hating on the idea...Well, not entirely!

I'm writing this as I'm in serious planning for a larger tank botanical pack, at the request of a number of hobbyists, so I'm certainly not biased against large tanks... Perhaps I'm a bit more biased against some larger fishes...However, what really makes me curious is this "I have a big tank so I HAVE to keep large fishes in it" equivocation that so many of us have in our minds.

And yeah, I have a custom-built 152 US-gallon, 40"x40"x22" tank in my garage, waiting for the right idea...and I've had 240 and 225 US-gallon tanks over the last decade as well, so this isn't written from the perspective of a guy who thinks a "40 breeder" is like, really freaking BIG! 

I mean, have you noticed that, typically, when an aquarist keeps a larger aquarium, say a 75-150 gallon (283-378L), the inhabitants are almost always larger fishes? Now, again, this is logical, right? If you have the capacity to maintain larger fishes in your aquarium, it makes sense. And of course, a lot of people maintain larger aquariums specifically to keep larger fishes!

Just like the "nano tank" crowd keeps tiny fishes in their little boxes. Duh. The "chicken-or-the-egg" theory, I suppose. And my favorite are the arguments put forth by some of my fish geek friends who proffer, "Keeping tiny fishes in a huge tank is just a waste of space!"

Urghh, how can I argue with that?

Just look at the facts:

Cichlids, like the Mbuna are typically on the larger side, or keep serious territories or social orders which require larger tanks. Arowanna and other large "monster fishes" flat-out need large amounts of physical space. Others produce a lot of metabolic waste, and larger tanks are required for environmental stability and disolution of said waste.

Discus and Angels simply need large spaces to accommodate their vertical morphology, etc. Even full-sized specimens of my beloved Knifefishes need large aquariums if you intend to keep them for anything close to a natural life span without imposing cruelty on them.

The ethical arguments are fairly clear here. 

I totally get it.

Well, wait for just a second. I get it, but let's think about the aesthetics, too. Let's look at the other side of the coin...

Why would you NOT keep lots of little fishes in a big tank? And why are the "big" fishes seen as "aspirational", and smaller little guys are just sort of seen as...well..."basic" or something.?

Have you priced Tucanichtys tucano lately? Cha-Ching!

Or, have you ever seen a school of 200 Cardinal Tetras in a large planted aquarium? Rasbora?  Or (if you like your characins larger) a shoal of Congo Tetras? For that matter, who has the balls to create a 100 gallon tank dominated by a school of Ruby Tetras or even those aforementioned Tucano Tetras (if you have the financial means, that is?).

It would be pretty amazing, and I'll bet that even a lot of small-fish-hater hobbyists will at least make a passing complimentary statement, like, "That looks pretty cool."

And to you fellow reefers out there, we pretty much all agree that smaller fishes in big tanks are the way to go, right? Wait, don't answer that...

Okay, where am I going with this tortured discussion?

Well, I'm just giving my occasional encouragement to do the "big tank/small fishes" thing once in a while. I for nothing else besides the sheer novelty, think about the impressive scale it would provide...I mean, a lot of little fishes in a well-scaped large aquarium can be a pretty realistic representation of a natural Asian peat bog, Igapo, or a section of an African stream or temporal pool.


You know, scaled-up versions of the smaller tanks we all play with.

There is no right or wrong. It's like arguing which color is better, blue or green (it's blue, BTW). 😜

I'm just curious who in our community is keeping, planning, or has kept a big tank with the little guys in it? Did you find it to be a "waste of space" like the argument goes, or was it/is it as impressive as I think it is?

In the end, it's all about what YOU like. What YOU want to keep. And most important, the needs of the fishes.

However, it is fun to ponder...And besides, small fishes are cooler. 

There, I said it. ✌️ Peace, out, mutha------s! 

Stay thoughtful. Stay curious. Stay opinionated...

And Stay Wet.


Scott Fellman

Tannin Aquatics 


Scott Fellman
Scott Fellman


2 Responses


February 28, 2023

I struggled with deciding what to keep in my newest 75 gallon for so long… I was getting told left and right that “that’s a lot of space for some guppies”

And I started looking at all them big old fishes that would take up almost all the space ALONE.

And decided no. I want a BUNCH of little fish of different species that will interact.

Now I keep ~ 35 glowlights, some neo shrimp, 20 Hasbrosus cory catfish, and 6 honey Gourami…. and 7 male guppies (and counting). I love my small fish. They move a lot, swim in patterns, never swallow eachother. Fun.

Robert Brown
Robert Brown

January 26, 2019

I kept large fish for years in my 75 gallon. One night my Red Face Cichlid shattered one of the heaters and every fish was electocuted. We thought about selling the tank. Too make a long story short we converted the whole thing to a planted tank with Tetra schools. We have 30 Neons, Cory cats, 6 Otocinclus, 10 Serpae Tetras and various others. I have to say I love the look and prefer it to larger fish.

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