A little clarity on...clarity?

As aquarists, we were pretty much indoctrinated from the start that our tanks should have "crystal clear, blue-white water", and that this is one of the benchmarks of a healthy aquarium.

And of course, I won't disagree that "clear" water is nice. I like it, too...However, I would make the case that "crystal clear" water is: a) not always solely indicative of "healthy" or "optimum" , and b) not always what fishes encounter in nature.


Of course, in the aquarium, cloudy water is often indicative of some sort of trouble- typically, bacterial blooms, algal blooms, incompletely washed substrate, etc, so we correctly make the initial assessment that something might be amiss when water suddenly becomes cloudy or 'murky", or just shows turbidity.

On the other hand, "turbidity", as it's typically defined, leaves open the possibility that it's not a negative thing:

 "...the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air..."  

What am I getting at?


Well, think about a body of water like the Rio Negro, as pictured above in the photo by Mike Tuccinardi. This water is of course, "tinted" because of the dissolved tannins and humic substances that are present due to decaying botanical materials.  That's different from cloudy or turbid, however.  It's a distinction that neophytes to our world should make note of. The "rap" on blackwater aquariums for some time was that they look "dirty"- and this was largely based on our bias towards what we are familiar with. And, of course, in the wild, there might be some turbidity because of the runoff of soils from the surrounding forests, incompletely decomposed leaves, current, rain, etc. etc.

None of the possible causes of turbidity mentioned above in these natural watercourses represent a threat to the "quality", per se. Rather, they are the visual sign of an influx of dissolved materials that contribute to the "richness" of the environment. It's what's "normal" for this habitat. It's the arena in which we play in our blackwater, botanical-style aquariums, as well.

Obviously, in the closed environment that is an aquarium, "stuff" dissolving into the water may have significant impact on the overall quality. Even though it may be "normal" in a blackwater environment to have all of those dissolved leaves and botanicals, this could be problematic in the aquarium if nitrate, phosphate, and other DOC's contribute to a higher bioload, bacteria count, etc. Again, though,  I think we need to contemplate the difference between water "quality" as expressed by the measure of compounds like nitrate and phosphate, and  visual clarity.

Our aesthetic "upbringing" in the hobby seems to push us towards crystal clear water, regardless of whether or not it's "tinted" or not. A definite "clear water bias!" And think about it: You can have absolutely horrifically toxic levels of ammonia, dissolved heavy metals, etc. in water that is "invisible", and have perfectly beautiful parameters in water that is heavily tinted and even a bit turbid. That's why the aquarium "mythology" which suggested that blackwater tanks were somehow "dirtier" than "blue water" tanks used to drive me crazy.

Color alone is not indicative of water quality for aquarium purposes, nor is "turbidity." Sure, by municipal drinking water standards, color and clarity are important, and can indicate a number of potential issues...But we're not talking about drinking water here, are we?

I've seen plenty of botanical-influenced blackwater aquariums which have a visual "thickness" to them-you know, a sort of "look"- with small amounts of particulate present in the water column, usually fines from decomposing leaves and other botanical materials- yet still have spot-on water conditions from a chemical perspective, with undetectable nitrate, phosphate, and of course, no ammonia or nitrite present.

It's important, when passing judgement on, or evaluating the concept of botanicals and blackwater in aquariums, to remember this. Look, crystal clear water is absolutely aesthetically desirable for 98% of all aquariums out there- but not always "realistic", in terms of how closely the tank replicates the natural environment. (And of course, by the same token, a healthy botanical- influenced tank may typically not be turbid, but that doesn't mean that it's not "functioning properly.")

Again, this realization and willingness to understand and embrace the aesthetic for what it is becomes a large part of that "mental shift" that we talk about so often here on these pages.

And the beauty of an aquarium is that you can either remove or contribute to the color and clarity characteristics of your water if you don't like 'em, by simply utilizing technique- ie; mechanical and chemical filtration, water changes, etc.

It's that simple.

I submit that the key takeaway here is that we should evaluate the "health" or normalcy of a blackwater, botanical-influenced aquarium-or ANY aquarium, for that matter- based on it's chemical water quality first and foremost, AND the clarity and color of the water on a secondary basis (Keeping in mind, of course, that the "aesthetic" of such an aquarium may indeed mean that turbidity and tint is perfectly normal).

A lot to think about on a relatively mundane subject- one which for many years was very "cut and dry."

Stay open-minded. Stay curious. Stay objective. Stay clear...or not!

And Stay Wet.


Scott Fellman

Tannin Aquatics

Scott Fellman
Scott Fellman


4 Responses

Scott Fellman
Scott Fellman

October 24, 2022

MMM- A good question…Not being a chemist really limits what I can postulate here!

I THINK that the tannins are perhaps not “attracted” to flocculants. Flocculation is a process by which a chemical coagulant added to the water acts to facilitate bonding between particles, creating larger aggregates which are easier to separate. What this all means to us, IMHO, is that tannins aren’t really “particles”, and they’re not really removed by this process…

Okay, that’s my theory, anyways!



October 22, 2022

I’m wondering if you could address what happens when you try to add a commercial water clarifier to a BW tank? I’ve seen a few people on forums turn their tanks into truly perplexing problems, the term “black hole” pops up a lot and it’s fitting.

I understand that the flocculation of humid substances and tannins are at play, and I grok that, but I’ve seen folks unable to clear it up with filtration of all kinds, and I’m curious. Maybe there is oxidation of something too small for mechanical filtration, and too persistent for chemical?

Reason #4732 why BW is the best — there is still so much that no one has figured out yet, so we all get to learn together ❤️

Scott Fellman
Scott Fellman

November 26, 2018

Hi Savannah,

I’m thinking basically two ways- you could use mechanical filtration (ie; some filter pads- perhaps a couple of layers) and some coarse mechanical media, like "Efi-Mech, neither of which will affect the “tint.” And, really, you could use some Purigen, Poly Filter or even activated carbon in limited amounts, all of which won’t take out too much tint if you don’t use a ton of the stuff..all of which can contribute to greater clarity! I use a combination of “micron filter socks” and Purigen/carbon and generally have clear, non-turbid water and that nice color we all love@ Hoep this helps!



November 25, 2018

im wondering if there is a way to reduce the turbidity (cloudiness) of my blackwater tank without removing the tannins or tint?? for aesthetic purposes i do want clear water… but maybe like amber clear, rather than crystal clear!

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