Last update: November 4, 2022

What the Heck Is the Aquarium Water Column?

You might have come across the phrase water column in online discussions.

That’s exactly how I stumbled across the phrase years ago, when I first entered the hobby.

And, when I googled:

What is a water column in aquariums?

It only brought up the water column in relation to oceans… Nothing related to aquariums.[1]

And, nothing there answered my question.

Years later, I see that this question still doesn’t have an online article dedicated to it – so I decided to write one myself!

What is the aquarium water column?

The phrase water column refers to all the water in your aquarium, from the top of your substrate, to the surface water – every last drop.

If your tank has no substrate, then the water column is from the bottom of the tank to the water surface.

To put it simply, the water column just refers to the water that sits inside your tank.

No pebbles, no plants, no fish, no aquarium equipment – just water.

It is important to note that when discussing the water column, it typically does not refer to water that sits in the pipes and filters.

If you were to draw imaginary lines in your tank, separating it into thirds, it would look like this:

The top, middle and bottom of aquarium water column diagram

That is the water column.

Not too difficult to understand, right?

I can understand where the confusion comes from… Below are two questions I came across in online forums:

1. How do I get rid of algae in my water column?

2. The water in my tank has algae, how do I get rid of it?

Well, it turns out that both of these people asked the same question.

My personal observation is that the term water column is more widely used by experienced hobbyists.

But the phrase ‘water column’ isn’t just used to identify the beginners from those who are more experienced…

It is also used when discussing exactly where a fish prefers to swim in your aquarium.

As you might have noticed with your own fish, different species prefer to swim at certain spots in your aquarium.

This is how the water column is most commonly used in discussion – in relation to where a fish spends most of its time.

Danios, Raspora and many Tetra, for instance, prefer the top level of the water column.

Angelfish, Platy and goldfish prefer the middle level of the water column.

And Pleco, Cory and Kuhli loach prefer the bottom level.

By paying attention to what fish swims in which section of the water column, you can build up an exciting community tank with fish inhabiting all areas of your aquarium – not just a single level. How cool is that?

Community tanks that take the water column into account are often much more exciting and pleasing to look at than those that don’t.


If you made it this far, you should now have a complete understanding of the water column. Now, use it in a conversation today!

Ian Sterling

I've been keeping fish for over 30 years and currently have 4 different aquariums – it's an addiction. I'm here to teach you everything there is to know about fishkeeping.

I also use this site as an excuse to spend lots of money on testing and reviewing different aquarium products! You can find my reviews here.

Comments (6)

Completely wrong I’m afraid, you really need to establish a good rapport between giving advice with regards to knowing the subject matter.

Hi Cyril,

Your comment provides no clarity and does little but insult. If you know better, then why don’t you share your expertise on the topic? I would love to know where the article went wrong so that I can improve it!


I’m not really sure why you made the statement that you did. This article simply describes what people are referring to when they speak about a water column. I think the post was clear and concise as well as being basic enough for a beginner to understand. I also liked the examples of where different fish like to hang out in the column.
Please explain your displeasure more.

*background on me* I worked for a company that builds, calibrates and instructs end users on deep sea test equipment for 7 years as a repair and calibration tech and as a traveling instructor. Can’t forget my 22 year as an M1A1 Abrams crewman but that isn’t as relevant to this discussion…

Hi Ian. I’m at my wits end. PLEASE. I cannot keep my 29 gal tank sparkling clear. I have done three water changes the first 75% the last two 50 %. My Ammonia is fine water has been tested. My suction tube has removed a lot of fish matter in the beginning and now that part is clean. I do have two artificial plants that were cleaned when purchased. There is no direct sunlight entering the tank and my tank light is on only for a few hours.

Hi George,

If you want truly crystal clear water you would need a filter capable of removing all the finest pieces of grit. Often called a polishing pad (50um) these can trap all the tiny bits of gunk that slip through your more coarse filter and can clean up the water, assuming it’s debris. If it’s free-flaoting algae, then you’ll gave to treat the cause. A UV sterilizer can help if that’s the case.

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