Return of the Archaens?

Okay, that literally sounds like the title of a Star Trek episode, but it's pretty good for our discussion today, I think!

"Beam me up, Scotty!"

(Okay., I had to...)

Every once in a while, I get an email asking about some of the more esoteric aspects of managing a blackwater, botanical-style aquarium, and it makes me realize that a) there is so much we have to discover as a community, and b) there is even more stuff that I personally am completely clueless about!

And that's okay!

In fact, it's awesome, because it means we are going beyond just tossing seed pods, leaves, and stuff into our tank and admiring the pretty brown water and cool aesthetics...we are thinking about the environment itself, and the interactions and processes which occur in our systems as they operate in this realm.

We're sort of "maturing" in this game.

The other day, a hobbyist contacted me about the process of nitrogen cycle management in the lower pH aquarium; how it works and how we could get a cycle going...And of course, it made me once again kick myself in the ass for sleepwalking through biology class in colleges...but it also got me thinking. Specifically, he was concerned that the "bacteria in a bottle" products that are available commercially for the purpose of kick-starting the nitrogen cycle in our tanks typically don't function at lower pH levels.

It got me thinking about the nitrogen cycle and how it works in our blackwater, botanical-style tanks, and the importance of going slowly, observing and testing, and understanding where the potential pitfalls can be which can (rarely) cause bad outcomes.

I mean, we all should have at least a rudimentary working knowledge about the nitrogen cycle and how it works in our aquariums. There are numerous articles written about that in hobby literature by people who have forgotten more about it than I'll ever know, so I'll assume you have that down..

Back to the "bad outcomes" parts:

It's incredibly rare, however, I think that the occasional bad outcomes we have had over the last few years (I can literally count the reports on the fingers of one hand..) are a result of misunderstanding or miscalculating the effects of identification and such in our lower pH, botanical-style blackwater aquariums.

I think it starts by pushing things too hard and too fast when we are dealing with very low pH aquariums- particularly new and/or biologically "immature" ones. What a lot of aquarists who run very low pH systems report is that the "cycling process" takes longer to complete.

This is an interesting observation, huh?

I know some pretty experienced hobbyists who don't even own an ammonia or nitrite test kit, and have long ago felt that the "need" to measure ammonia or nitrite has been eclipsed by their experience, so they have no way of correlating this to the (admittedly rare) "disasters" which befall their  low-pH systems...tsk, tsk.

And the longer "cycle time?"


This definitely correlates with my personal findings, although I've personally never managed a system with a pH much below 5.5 pH; this is where the "outer limits" of low pH aquariums starts for most, and this is likely the realm of Archaea, as the Nitrosomanas and Nitrobacter barely function at that point. We've seen advanced aquarists depend upon chemical filtration media to manage organics at these extremes.

And once again, I think that the real key ingredient to managing a low pH system (like any system) is our old friend, patience! It takes longer to hit an equilibrium and/or safe, reliable operating zone. Populations of the organisms we depend upon to cycle waste will take more time to multiply and reach levels sufficient to handle the bioload in a low-pH, closed system containing lots of fishes and botanicals and such.

This certainly gives the bacterial populations more time to adjust to the increase in bioload, and for the dissolved oxygen levels to stabilize in response to the addition of the materials added-especially in an existing aquarium. Going slowly when adding are botanicals to ANY aquarium is always the right move, IMHO.

And at those extremely low pH levels?

Archaens. They sound kind of exotic and even creepy, huh?

Well, they could be our friends. We might not even be aware of their presence in our systems...If they are there at all.

Are they making an appearance in our low pH tanks? I'm not 100% certain...but I think they might be. Okay, I hope that they might be. 


Archaeans include inhabitants of some of the most extreme environments on the planet. Some live near  vents in the deep ocean at temperatures well over 100 degrees Centigrade! true "extremophiles!" Others reside in hot springs, or in extremely alkaline or acid waters. They have even been found thriving inside the digestive tracts of cows, termites, and marine life where they produce methane (no comment here)  They live in the anoxic muds of marshes (ohhh!!), and even thrive in petroleum deposits deep underground.

(Image used under CC 4.0)

Yeah, these are pretty crazy-adaptable organisms. The old sayings that "If these were six feet tall, they'd be ruling the world..." sort of comes to mind, huh?

Yeah, they're beasts....literally.

Could it be that some of the challenges in cycling what we define as lower ph aquariums are a by-product of that sort of "no man's land" where the pH is too low to support a large enough population of functioning Nitrosomanas and Nitrobacter, but not low enough for significant populations of Archaea to make their appearance?

I'm totally speculating here. I could be so off-base that it's not even funny, and some first year biology major (who happens to be a fish geek) could be reading this and just laughing...

I still can't help but wonder- is this a possible explanation for some of the difficulties hobbyists have encountered in the lower pH arena over the years? Part of the reason why the mystique of low pH systems being difficult to manage has been so strong?

Could it be that we just need to go a LOT slower when stocking low pH systems?

Perhaps. Yeah, probably.

And then- you think about the pH levels in some natural, well-populated (by fishes!) blackwater habitats falling into the 2.8-3.5 range, you have to wonder what it is that makes life so adaptable to this environment. You have to wonder if this same process can- and indeed does -take place in our aquariums. And you have to wonder if we simply aren't working with these tanks in a correct manner.

Particularly, when they fall into what we'd call "extreme" pH ranges. I wonder if the "crashes" and fears and all sorts of bad stuff we've talked about in the hobby for decades were simply the result of not quite understanding the "operating system?"

Things just work differently at those lower pH levels- in nature, and in our aquariums.

I think the secret is out there somewhere.

And I can't help but speculate if the key to success with these low pH systems lies in understanding the functions of...

The Archaens.

Stay curious. Stay bold. Stay resourceful. Stay engaged...

And Stay Wet.


Scott Fellman

Tannin Aquatics 




Scott Fellman
Scott Fellman


1 Response


October 09, 2022

We need another follow up to this!

Linked the article here:

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