The crowd? Or just the community?


One of the great things about being in the aquarium hobby for a lifetime is that you have numerous opportunities to learn things, acquire new skills, sharpen old ones, and to occasionally re-think stuff you thought was not even questionable in the past.


For example, stocking our tanks.

When it comes to stocking aquariums, I've historically been extremely conservative, erring on the side of under-stocking, and simply leaving a a lot more room for additional fishes in most of my systems over the years. I would often be teased by friends about how "empty" my tanks looked, lol.

I think that part of this conservative trend comes from my aquarium upbringing. My dad bred fancy guppies, and was himself brought up following the teachings of the legendary masters of the guppy hobby, like Hahnel, Sternke, and Alger, who advocated moderate stocking of their guppy tanks, for a lot of good reasons.

I grew up reading all about them as a kid in my dad's old aquarium books, and applied their ideas to my work, too.

Some of my attitude towards stocking was based upon the technology I grew up with in my earliest days in the hobby. Inside corner filters, outside power filters, and under gravel filters were thought to have a rather limited "capacity"...for what, I'm not exactly certain, but nonetheless, I followed the "rules of the day" when it came to common sense stocking.

Of course, when I was a teen, we had the dawn of the modern reef aquarium hobby, and its evolved practices and technology, which I have since spent decades playing with. The advent of trickle ("wet/dry") filters, evolved protein skimmers, and the practices of utilizing live rock and sand in reef tanks changed the game. A marriage of biology and technology as never before. It kept evolving to this day with sumps, calcium reactors, dosing systems, LED lighting, and now, with automatic filter rollers.


Suddenly, not only could you keep delicate organisms like stony corals alive, you could keep more of them, because of the practice of building up an ecosystem- a "biological infrastructure", if you will- which included a heavy reliance on beneficial bacterial populations and managing the specific physiological needs of these organisms.

I was still a bit conservative in stocking for quite a few years; typically massively over-building nutrient export mechanisms and practices into my systems. They definitely served me well, even though, looking back, I think I was traversing deeply into "overkill" territory!  It wasn't until quite recently that I really began to question why I was so conservative, and for what reasons. "Cleanliness" (for want of a better word) was, for many years, seen as the way to get great results.

The reality of this over-simplified mindset on near-sterility eventually made me realize I was wrong. When I was a partner in a coral propagation facility, early on it became increasingly obvious that the desire to literally polish the shit out of the water had the opposite effect on the corals. We were simply making the water too "clean!" Only when we allowed some nutrients to accumulate, and relied more on natural processes than "technology overdrive" did our corals start to really thrive and grow faster.

And, this definitely had an impact on my freshwater practices.

In 2015, when we started Tannin Aquatics, we pushed heavily on the idea of using botanical materials to help create a functional biome- an ecosystem- to facilitate nutrient processing and supplemental nutritional resources for our fishes and other organisms that reside in our tanks. I spent a lot of time studying and researching the wild aquatic habitats which enthralled me. Married with a more "holistic" approach, which views the aquarium itself as a "filter" of sorts, my conservative approach to stocking began to evolve and liberalize considerably!

So here we are today, with me talking about a totally different mindset on stocking your botanical-method aquariums. I needed to provide you with that brief history of my hobby experience on the topic to provide some context, and to reassure you that I'm not just some asshole telling you to "stick it to the man" and blow off a century of aquarium hobby "best practices" just..."because!"

Now, before I get into the meat of today's topic, let me clarify a few things. I am NOT calling bullshit on the idea of common sense in aquarium management. I am NOT advocating that everyone fill their10-gallon starter tank with 50 Neon Tetras, or other equally stupid things. 

I am still a firm believer in NOT over-stocking your tank.

I just think that the "limits" are farther out than we have previously assumed. Yeah, I wonder, what exactly is the definition of "over-stocking" anyways? Is it a sort of subjective thing?  Or, some hard-and-fast "number?" Is it a tank that simply looks ridiculously full of fishes? Or is it a "thing" that is determined by water quality (ie; nitrite, ammonia, nitrate, phosphate, etc.) or other environmental factors which are measurable (pH, conductivity/ORP, dissolved oxygen levels, etc.)?

Likely, the latter.

I don't profess to have the authoritative answer to every aspect on this topic. I can only share what works for me; where I've come from, how I reached this point, and what it has done for the fishes which I keep. Again, there is likely as much subjectivity as there are obvious answers to stocking methodology.

I mean, on a superficial level, there is not a lot of difficulty in calling bullshit on the idea of stocking a full-grown Clown Knifefish, a large Pleco, and an adult Oscar in a 20-gallon aquarium, right? The physicals pace and physiological ability of the tank to support that much life is obvious. The amount of metabolic wastes they produce would literally overwhelm virtually any practical filter or biological processing system which you could attach to such a tiny tank, in hours. And not to mention, it's simply cruel to keep these fishes in a tiny space like that..sort of like having to spend the rest of your life in a closet with 3 adult strangers!

This kind of overstocking should be obvious to all.

And I'm not talking about trying to stuff 80 Mbuna in a 50 gallon tank, or whatever. Fishes which have significant space needs because of their territorial behaviors or "pecking orders" typically don't play well with this concept. I've heard the theory that the "overcrowding" lessens aggression or whatever... I disagree, as substituting once stress for another is not a good thing.

What I'm talking about specifically here is figuring out how many small (and by "small", I mean fishes that are 1"-1.75" or so in length, like characins, Rasbora, etc.) can be kept healthily, humanely and safely in that same 20-gallon aquarium. 

Consider fishes like characins. Okay, the small ones, like Hyphessobrycon, Hemmigrammus, etc. Not fucking Pacu or Piraniah, etc. 🤬

How much metabolic waste does a fish that weighs a gram or so actually eliminate into the aquarium on a daily basis? I'm sure there is a study of that...somewhere. I'll bet that if we knew the actual numbers, a lot of minds would change on stocking. 

Of course, there are also the most banal of considerations when talking about more densely stocking your, aesthetics. I mean, do 50-100 fishes of ANY type and size look good in ANY type of aquarium to you? Do you actually WANT that many? Or, can you afford that many? I mean, 100 Tucano Tetras, for example, can set you back a serious amount of cash!

But yeah, lets stay on the general topic of characins....

Many of these little characins occur in large shoals or schools in Nature. That's how they live. They've evolved to live that way. They feed together, shelter together, and spawn together. As a community group. They are often gregarious and social, and display their most natural and healthy behaviors when kept in such groups. They feel safer that way. These little fishes are almost like a single, communal organism!

They will generally simply fail to thrive, or at least, be at their best- when not kept with a significant number of their own kind in an aquarium setting. There is a legitimate reason why keeping 1 or 2 Cardinal Tetras in a so-called "community tank" is just not good. You're often told to keep "at least 6-10 specimens or more together" for them to be at their best.  

It's the "or more" part that intrigues me, of course. It's logical. There is a reason for that, as we just discussed.

They live in large groups in Nature. Fact.

I mean, yeah, you're limited by the size of your tank, 'cause it's not the Igarape Dracua in Brazil or wherever. It has no large water "flow through", or a vast supporting terrestrial ecology. It has different external environmental inputs, and a finite amount of water. So your job as an aquarist is to find that "sweet spot"  which provides your fishes the ability to live their lives in social and physical comfort, while maintaining acceptable water quality. That means keeping them with a significant enough population of their peers to meet their needs, while keeping water quality and health at optimum levels.

I actually see this challenge as a call to simply add more fishes to our tanks, when permissible, and to create environmental conditions appropriate for them to thrive.

The two need NOT be mutually exclusive.


Now, look, once again, this is not a call to run off, like the proverbial "headless chicken" to the LFS and buy 300 Cardinal Tetras for your 50-gallon tank. That's just dumb. It IS a call to consider if that 50-gallon tank can be created and managed in such a way as to responsibly provide a healthy, sustainable home for say, 50-75 of those same Cardinal Tetras. 

I think that it can be. And this is not one of those things that I'm pushing out to be "in your face"; to garner those comments like, "Sure you CAN, but why WOULD you?"

It's not like those, "I do THIS and never do water exchanges!" kinds of asshole-like ideas which provoke nasty discussions on forums and Facebook groups. I'm not advocating some sort of "workaround" to best Nature here. I'm advocating looking at what occurs in Nature and figuring out if we can replicate some aspects of it in the aquarium, for our fishes benefit.

It's about creating conditions to maintain appropriately-sized populations in our aquariums. Now, sure, there are studies out there of wild aquatic habitats and their fish population density and diversity, where transects of wild habitats have been conducted, which, if you do some algebraic calculations, could yield some approximate numbers of fishes of a given species per a given area. Again, as I just alluded to, there is more to it than just "X" fishes per square meter", or whatever-but it is a starting point, right?

I mean, if the fishes have so much room in Nature, why do they congregate together in such large numbers in a small area?

You need to take into account your ability to provide an aquarium environment and maintain husbandry practices which can facilitate more dense population of fishes. I don't take this responsibility lightly. You shouldn't, either.

I am an extremely careful feeder, believe in good oxygenation and I am a champion of significant nutrient export (ie; water exchanges and use of biological/chemical filtration media, etc.) in all of my tanks.

The idea of building up a substantial (okay, let's change the adjective to "significant") population of little characins was something I'd always wanted to do over the years. However, I spent way too much time buying into "conventional aquarium thinking" and limiting myself to "1-inch of fish per gallon", or whatever the prevailing "guidelines" were at the time, to even think about challenging that.

And then, over time, I sort of started thinking about the rationale we employ for limiting stocking in aquariums: To create environmental conditions conducive to fish health. I realized that there is more to it than just listing the numbers of fishes. I believe that  you can actually have way more than the "one inch of fish per gallon" thing and still provide optimum environmental conditions...if you understand what those are for your fishes, and make achieving them part of your whole system from day one, and husbandry routine thereafter.

So, as I built up my population of 70 small characins in a 50-gallon tank, it occurred to me that it works because I do the things necessary to make it work. You can't have a large population of fishes in a given tank size without proper circulation, filtration, a water exchange regimen, and careful feeding. Give-and-take. Like everything in this hobby. You can't "have it all." But you CAN have most of it! If you're flexible and willing to compromise.

I firmly believe that a botanical method aquarium, with its significant and well-thought-out emphasis on ecology, is the perfect starting point for a densely populated tank. As I've shared with you often, my thinking has long been that you should actually consider the tank itself (or more properly, the botanical environment within it) as the"biological filter", and simply use aeration/surface skimming and/or circulation pumps to facilitate the gas exchange.

After almost 25 years of playing with this botanical stuff, I'm convinced that the microbiome provided by a properly set up and managed botanical method aquarium provides a huge amount of biological support for the fish population. Not exactly revolutionary, of course- but an idea that's often overlooked today.

Think about this:

The botanical materials present in our systems provide enormous surface area upon which beneficial bacterial biofilms and fungal growths can colonize. In addition to physically fragmenting botanical materials, these life forms, collectively referred to as "epiphytes", utilize the organic compounds present in the water as a nutritional source. They also provide supplementary/primary food sources for a huge array of organisms within the aquarium itself, including the fishes.

Just like what happens in Nature.

In the case of our fave aquatic habitats, like tropical streams, ponds, and inundated forests, epiphytes are abundant, and many fishes will spend large amounts of time foraging the "biocover" on tree trunks, branches, leaves, and other botanical materials.

The biocover, as I just mentioned, consists of stuff like algae, biofilms, and fungi. Nature's "filters." Although most fishes use leaves and tree branches for shelter and not directly as a food item, grazing on this epiphytic growth which occurs on them is very important. You're unikely to have fishes in an aquarium decimate all of this growth, so a sort of "balance" is achieved.

Yeah, as I've said a million times here, I am of the opinion that a botanical-method aquarium, complete with its compliment of decomposing leaves and seed pods, can serve as a sort of "buffet" for many fishes- even those who's primary food sources are known to be things like insects and worms and such. Detritus and the organisms within it can provide an excellent supplemental food source for our fishes!

These organisms also provide a sort of "onboard nutrient processing" service for the aquarium in which they reside. A "filter", if you will...but one with a "feature set" and capacity far in excess of most commercial filter systems you can buy. It's free, and super reliable.

You just need to give it what it needs in order for it to work.

So, like, your filter is almost "supplemental" in this role, really. Think about it:  In most filters, you're trying to recruit bacteria and other microorganisms to help process metabolic wastes from your fishes. Well, as we just alluded to above, the biome within the aquarium itself does the bulk of that work, really.

The type of filtration, or more important, the quantity of filtration, and the way in which water is returned- together play a huge role in supporting a significant fish population on a long-term-sustainable basis. No real magic here. Nothing new..except a different understanding of the role that the "filter" plays in the aquarium.

Your aquarium should have some water movement, to facilitate gas exchange, provide a little "exercise" for your fishes (that sounded stupidly quaint, but you get the picture), and to avoid the formation of thermal, pH and/or nutrient layers in our tanks.

Gas exchange (the process in which carbon dioxide exits into the atmosphere and new oxygen from the atmosphere is dissolved into the water) is really important in aquariums, and aeration from filter returns helps facilitate the process. Fish need oxygen (like 5-6 parts per million) in their water. Now, it's not mandatory to have airstones, filter returns, or surface skimmers to create surface agitation, but it sure helps, particularly if you keep a large population of active fishes! 

I suppose you could say that the "purpose" of aeration is to "break up" the surface of your water. You’re not going to separate the oxygen molecules from the water and force a gas exchange within the water column, by cranking up an ayirstone- that's not what it does. But it will help break up the surface boundary layer to facilitate gas exchange. I guess that's why I love surface skimmers, or filters which skim the surface boundary layer. They just make the gas exchange process easier and more efficient.

And of course, simply choosing an aquarium with a large surface area is important and beneficial, too. Wider, more shallow tanks are always better than tall narrow ones at this.

What about foods- and the way we feed our fishes? 

Feeding is, of course, very important. As is the type of food, the frequency, and the amount dispensed.

As a long-time proponent of primarily feeding frozen foods to my fishes, I realized that frozen is not the panacea that it seems to be. Sure, there are certain benefits to being able to feed fresh stuff like brine shrimp and worms and things in a convenient fashion. However, frozen foods also often have a significant amount of organic material- stuff you may not want in your tank- with the food as a part of the process of manufacturing them.

The "juices" contained in them, which, when added to the aquairum water can lead to accumulations of nitrate and phosphate- the "enemies of high water quality"- within the aquarium if you're not especially fastidious. It's easy to literally "kill your fishes with kindness!"

I think that, if you're trying to push the fish population a little, careful, non wasteful feeding becomes really important. This would necessitate a change to other foods- like pellets. Yeah, I admit, I used to hate pellet foods. I thought they were sort of nutritionally-defficient "kibble" for fishes. And most of them were- back in the day!!

Fast-forward to now...There are some amazing, super high-quality, highly nutritious pellet foods out there which are easy to feed, contain almost no fillers or non-nutritious ingredients, and which are easily digested, encourage more uptake of nutrients and less metabolic waste, and can be fed in such a way as to assure that less goes "down the drain" as opposed to in your fishes' mouths.

Can you still use frozen food in a more densely-populated tank? Of course! I do! Just be more careful. Don't feed it every single day, multiple times a day, in large amounts.

Little compromises. Changes in the way we do stuff. We know how to work with that.

And one other thing...You won't just dump the entire population of your fish into the aquarium from day one, right? I mean, you shouldn't. At least, not without some preparation. You need to allow the resident beneficial bacterial/microbial population to build up to handle the increase in metabolic wastes produced by the fish population.  Slow advance of adding the fishes.

Okay, building up a population of beneficial bacteria to tackle the metabolic waste products produced by your fishes is decidedly conventional  aquarium hobby thinking. And there ARE some (oh, shit...) "hacks" that, in theory and practice, could make it possible to add a LOT of fishes from the "get go". Intrigued? Well, you know the "hack" I'm gonna talk about. It's called, "pre-stocking." It's pretty straightforward, but it requires time. And patience! (shocker, I know. Only my "hacks" would not really be "hacks". Or not "time-saving" ones, at least...)

Here's the deal:

Set up a botanical method aquarium with a large number of leaves and other botanical materials and substrate from day one. Inoculate with live bacterial cultures (PNSB and/or Nitrobacter/Nitrosomanas). Throw in a bit of fish food if you want. Stock with organisms like Daphnia, Cyclops, Paramecium, etc. Let the tank "run in" for several weeks, or a month or more if you can handle it (you can). This will give the microbiome and overall ecosystem a chance to literally arise and "assemble itself" before the fishes are added!

Then you could add most, if not all of the fishes at once. Seriously. 

Is there a risk to this? Well, sure. Working with live animals in a closed aquarium always involves some risks. No guarantees. You could still lose fishes. And you still need to monitor nitrite and ammonia, and to understand the concept of the nitrogen cycle. You need to be aware and do a little work. I've done this exact thing literally several dozen times in the past 20 or so years, including just a few weeks back, BTW) and have never, ever had either detectible ammonia or nitrite, let alone a "cycle" after adding the fishes. Other than a few "jumpers", I've seldom lost a fish to this process.

Yeah. I'm no fucking visionary. And I'm not the only hobbyist who's done this. Plenty of botanical method aquarium enthusiasts employ this  same practice with similar tremendous success. I mean, it shouldn't be a real surprise, because it's not really a "shortcut."  It's not some "miracle." It takes time!  That's the compromise you have to make. You're simply establishing the ecology and the nitrogen cycle within the tank before the fishes arrive. "Fishless cycling" as the process is known, but with a botanical-method twist and it's associated benefits!

This is also nice because it slows you down ahead of adding the fishes, and gives you time to acclimate and quarantine all of your fishes before releasing them into the display aquarium. It also has the advantage of starting your fishes in an aquarium which is, by many hobby definitions, very well "established" before they're ever added! Other than the "adding most of the fishes at once" part, it's actually not all that different from gradually stocking a tank over  time, except that a more robust ecology was in place and operating long before the fishes arrived.

And of course, you could employ the same mindset, yet gradually build up a fish population anyways- perhaps for other reasons- like getting the more timid fishes settled in first, before the active, crazy ones, etc. Apply it in a manner that works for your situation.

And of course, perform regular water exchanges on your aquarium. Make them a ritual. Regardless of how comprehensive the ecology in your tank is, it's not an open, natural habitat.  It requires proper care. If you're going to ply new territory, don't abandon all of the tools that got you there in the first place. You're smarter than that. I know that you are!

So yeah, THAT is how I have 70 healthy, happy, and active little fishes in my 50-gallon aquarium. I didn't "cheat." I didn't create some dependency on a huge and absurdly complex commercial filter system, or some magic elixir. I'm not slave to massive water exchanges daily. All I did was think about how ecology works in aquatic systems, partner up with Nature, deploy all of the things we've talked about in our botanical method aquarium work for years now, and provide the optimum conditions to allow a (dense) population of fishes to thrive from day one in my tanks.

I compromised when required, and understood many of the nuances involved in keeping large groups of fishes. I studied what occurs I the wild and figured out how to make it work in my aquariums.

You can, too.

It's literally another mental shift. An example of looking at things from (as we say here) a slightly different perspective...

Again, some of you may disagree with this approach vehemently. Some of you may be like, "WTF, Fellman. Freaking irresponsible." Some of you might shrug and say, "Okay, yeah. Whatever. So?" A certain percentage of you might have already thought like this. A smaller percentage may just give the approach a try in the future.

I encourage you to do what you think is best for your fishes.

Regardless of how you stock your tanks, study some of the science behind it. Understand the nitrogen cycle, and the importance of building up an ecology in your aquarium. Shift to considering the entire aquarium a miniature ecosystem, capable of supporting a vast array of life at many levels. Study the needs of your fishes, and figure out the best way to meet them.

Don't take shortcuts for the sake of "gaming the system" (ie; Nature). The "system" will simply kick your ass (and kill your fishes in the process). Don't just take my words as "gospel" here, nor the guy with 40,000 followers on YouTube, the Instagram "influencer", or your cousin Brian.  

Think it through for yourself. 

Responsibly experiment.  That's really the only way to advance this hobby. 

Sorry, Brian.😆

Stay curious, Stay bold. Stay thoughtful. Stay experimental. Stay logical. Stay grounded...

And Stay Wet.


Scott Fellman

Tannin Aquatics 




Scott Fellman
Scott Fellman


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