Guide to Iwagumi Aquaria

Posted on June 27, 2012 | 2 comments

Introduction to Iwagumi

The Japanese term “Iwagumi” literally means “rock formation.” In a Japanese rock garden, the rocks are the “bones” of the layout and usually consist of three or five rocks; one main or large rock flanked by two smaller rocks, but not of equal size. When the rock formation is placed properly, the rest of the layout will simply fall into place.

Each rock used in Iwagumi has its own name. There are special rules of Iwagumi, such as the way its substrate is laid and the order of rock placement. This article discusses the basics of Iwagumi that every reefscaper should know.

If you want to have your own Iwagumi Aquarium, Contact us. We can Design, Think Out and Build your dream tank. More info about our services you can find here.

In an Iwagumi aquascape you should always use an odd number of rocks of various sizes (three, five etc). One of the more difficult aspects of the Iwagumi Style is achieving visual balance through the aquascape. Many aquascapers follow the “golden ratio rule”, or the “rule of thirds”. These are two different things, although many think they are the same.

When you’re planning out an aquascape, one of the most important aspects is where it will draw the viewer’s gaze. In fact, a viewer’s gaze is what the aquascape is all about. The primary goal of an aquascape is to be pleasing, relaxing, and interesting to look at for the viewer. In order to do so, you need to set a sort of “anchor” for the mind. This is called the focal point. It is the point that draws the gaze of the viewer first, from which they can explore the rest of the tank. A focal point can consist of almost anything, from a large tabling or branching coral to a overhang with Zoanthus species. The only thing it must do is draw attention. You have to make it stand out in some way. There are a few simple things to remember about a focal point.
First, there should only be one. Having more than one focal point leaves the mind uncomfortable and stressed, looking back and forth from focal point to focal point. Only in extremely large tanks may you can have two focal points comfortably. Second, you should have some sort of focal point in every aquascape. Not having any does the same as having too many: the viewer’s eyes are left wandering back and forth, stressed and uncomfortable. Third, the focal point should be placed in a very particular (and special!) location. This is where we come to the Golden Ratio of aquscaping.

The Golden Ratio

The Golden Ratio is described as “two quantities are in golden ratio if the ratio of the sum of the quantities to the larger one equals the ratio of the larger one to the smaller. The golden ratio is an irrational mathematical constant, approximately 1.6180339887.” Simply put, the golden ratio is about proportion and the size and placement of one element compared to another. With the golden ratio if we look at an element we determin the ratio of one section to the other (in this diagram the left hand section compaired to section 1) we arrive at the size based on both the height and width of the element (of which are equal when removing the left hand section) and it is not determined by a ratio of a third. This rule specificly deals with astheticly pleasing proportions and ratios between two elements.
This Golden Rule dates all the way back to the Greeks. It seems the they came up with a theory that the ratio 1:1.618 was the most pleasing to the human eye. Many people assume that placing the focal point in the middle is most pleasing, however, this will again keep your eyes wandering left and right. By placing it slightly off center, you are effectively gently guiding the viewer’s eyes. You’ll see this Golden Rule used in all forms of art, from paintings to architecture. But how do you use this Golden Rule in the aquarium?
You need is a measuring tape (or ruler) and a calculator. Simply measure your tank lengthwise from one end to the other. Then divide that number by 2.618. Then divide the length of the tank by 2.618. This is where your focal point must be created (on the more left or more right side).

The Rule of Thirds

The rule of thirds however deals with a whole different design theory. The rule of thirds instead is a way to place elements with in a design as a way to control where a viewers eyes will travel and what they will see. “The rule states that an image should be imagined as divided into nine equal parts by two equally-spaced horizontal lines and two equally-spaced vertical lines, and that important compositional elements should be placed along these lines or their intersections.”

The idea is that by placing and arranging elements with the rule of thirds in mind will create a more interesting design and that a users eyes will flow through the intersections of the grid thus creating a design that has more energy and tension.

You may have noticed that this description of the rule of thirds does not talk about nor focus on proportion. You may also notice that an element taking up two out of three columns does not equate to the mathematics that determine the golden ratio.They are two completely different rules.

The Art of Rockscape

There are four basic stone types used in Japanese rockscaping . These are used in a thousand different combinations, but with the understanding of these basic types and some common usage, we can find the right ones for our aquascape.


This is the primary rock in Iwagumi. It is the largest rock as well. Select the best one in terms of shape and character. Its height should be approximately 2/3 of the height of an aquarium.


This is the second largest rock and is placed on either left or right side of the Oyaishi. Select a rock with the same or similar texture as Oyaishi to give uniformity to the overall Iwagumi.


It is smaller than Fukuseki and is placed next to the Oyaishi, along with the Fukuseki. It plays a key role in the flow that the Oyaishi creates by bolstering the presence of the Oyaishi or accentuating the strength of Oyaishi.

Suteishi (a sacrificial stone)

It is a small rock that does not stand out in the overall arrangement of Iwagumi, and it may even become hidden by aquatic plants occasionally. Its presence has a subtle, simple elegance.

These basic stones are used in any number of combinations and are often combined with Helping or Throwaway stones, smaller nondescript rocks that need not fit any of our formal definitions. Two and three stone groups are the norm and can be combined together to create larger focal points. There are five stone groups that are usually the main focus of a garden, often in the guardian stone position; this is a very powerful grouping and needs careful balancing.

Koya Garden

When you start to aquascape it is important to have more then enough Liverock at hand. This gives you more options when creating your aquascape, and you won’t be limited by a small selection of rocks. The rocks that you don’t use can be put in the sump to serve as extra biological filtration, of as cryptic refugium. I recommend having at least seven different sized rocks to select from. Find rocks that have character, the more nooks and crannies your stones have the more detailed and complex your layout will appear. When put arranged in an aquascape the rocks will appear as a unified collection while still maintaining their own distinct characteristics. The arrangement of the hardscape should have a clear focus and dictate the viewers’ perspective.

Royan-Ji Garden, Kyoto, Japan

The Final Goal

Iwagumi style should give you a feeling of tranquility and simplicity; therefore a limited number of coral species are used. Concentrate on fewer species that are interesting together because of color and coral morphologic (growth forms). Combining tabling species with some Staghorns can be a good choice for example.

When selecting fish you want to emphasis simplicity, harmony, and unity between the fauna and the aquascape. Too many fish species can cause discord and chaotic random movement among the fish, which distracts from the aquascape. For instance, a large number of Tangs or Anthias is not preferred.

Instead use a single species of schooling fish to add fluid movement and contentment to the aquascape. The most common used species are Apogon or Chromis species. It is important to use “schooling” fish and not “shoaling” fish. This helps to maintain a more tranquil environment.

True schooling fish from the Apogon family can help creating a tranquil admosphere
Royan-Ji Garden, Kyoto, Japan

Before you start to aquascape, I suggest to read a few books about Japanese gardens. A great book to start with is the book “Japanese Gardens” by Günther Nitschke from Taschen. I’m sure you will enjoy it and get many ideas and inspiration out of it.

Take a look at my latest reef tank Design, Apogon Reef for an example of Iwagumi in a marine aquarium. Also take a look at this video that explains and shows beautiful examples of the Golden Ratio in nature.

Royan Ji Garden images by|Reder|Kamoda|CC
Aquarium Image by |ADA
If you enjoyed this post, please consider leaving a comment or subscribing to the RSS feed to have future articles delivered to your feed reader.


  1. Very well written article. I appreciate the depth in which you explain the principles of Iwagumi. I am currently trying to create a nano tank, Iwagumi layout, myself and came accross this article when doing my research. Two thumbs up! Thanks.

  2. Thanks Jason! Keep us updated on the tank progression!


  1. Iwagumi aquascaping? - Page 2 - [...] that leave waste etc it's not for the novice aquarium keeper It's all about The Golden Rule…

Leave a Comment

Your email address will not be published. Required fields are marked *