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2hr Guide to Iwagumi aquascapes

May 28, 2024 10 min read

2hr Guide to Iwagumi aquascapes

Seiryu rock aquascape with dwarf hair grass (Eleocharis acicularis)


Iwagumi layouts are rock focused planted aquariums inspired by Japanese and Chinese rock gardens and by Japanese/Chinese rock appreciation - (水石) Suiseki in Japan and (供石) in China. Its goal is to showcase particularly aesthetic pieces of rock; rocks that have interesting weathering patterns or shapes make good candidates for such aquascapes.

In its most purist style, Iwagumi layouts use only a single type of rock and plant, and would usually consist of an odd number of aesthetically pleasing rocks (3 to 9 pieces). The rocks will be arranged in a format where the smaller rocks echo and compliments the textures and directionality of the main rocks. A single type of plant will usually be planted around the rocks to fully carpet the tank.

The modernist approach is more complicated - main rocks are blended with smaller rocks to give a more naturalistic transition from larger rocks to substrate. Instead of single rocks, larger rock formations and rock ridges can be constructed. Instead of planting the entire substrate, areas may make use of cosmetic sand instead, and rather than just using a flat substrate, the landscape may be sculpted into hills and slopes. Even the plant selection may be more varied - with mixed species of plants used instead of a single species.

Iwagumi aquascape by Jurijs

Guide to rock selection

1. Size of main rocks

The largest rock pieces in a tank should be at least 3/4 of the height of the tank, if not more to create a strong impression. The bottom couple of inches of large rocks are usually buried in the substrate to give the impression that the rocks rise naturally from the ground. Tilting rocks to get a more aesthetic angle also diminishes the final height of the rock. Most hobbyists use rocks that are far too small - underestimating the size required for hardscape to stand out in the tank.

Smaller rock pieces can also be connected together to form a larger rock formation. However, this process can be tedious and require a fine eye for matching up rock textures of separate rock pieces.

In this example, we use a rock about half the height of the tank. The rock shrinks visually after being placed in the tank. The hardscape will shrink further as the carpet grows and covers the bottom of the rocks. The final hardscape is far too small for this tank size.

In this example we switch out the rock for another piece that is 3/4 the height of the tank. After being placed in the tank, the rock is large enough to make an impact - however, after the carpet has grown in, the hardscape will probably be just large enough to hold its ground. What seemed like a huge piece of rock outside the tank turns out to look just averagely sized after being used in the aquascape.

We try switching out the rock for an even larger sized piece that is around 80% of the height of the tank. Tilting the rock to get attractive shadow reduces its final height significantly. Even so, this rock carries good weight in the final layout and will stand out even after the tank is fully grown in.

2. Shape, Texture

Triangular pieces are more easily arranged compared to squarish or round pieces, but do not let this limit your creativity. Rocks with unique textures and shapes are best candidates as the main rocks, however, rocks with very unique shapes and textures are harder to match. Finding rocks with matching textures are important for the entire aquascape to come together as a whole. 

3. Variety of matching rock sizes

In nature, larger rocks are constantly breaking down into smaller pieces. Where there are large rocks, there will usually be smaller rocks of a similar type. Having a mix of smaller sized rocks is very important if you are doing a more modern style Iwagumi where larger rocks transition smoothly into smaller pieces. This is especially so for Iwagumis where sand portions are used. Smaller pieces are necessary for the natural looking transition of larger pieces to substrate. Some rocks types (Ohko, lava rock, Slate) are easily broken down to smaller pieces using a hammer. Other types (Seiryu, Limestone, Granite) are very hard and difficult to break down manually.

Arrangement Tips

Not all the views of the same rock are equally aesthetic. The rock may also look best at an angle that is not its naturally resting angle. Smaller rocks can be used to prop up rocks to expose their best face to the frontal view. Cracks, interesting rock textures and other aesthetic features make for good focal points.

More significant rock pieces should be tilted at an angle so that the downward facing rock face is cast in shadow.  This shadowed face gives great contrast to the brighter surfaces directly facing the light and give the rock a more 3 dimensional look in photographs. Shadows will also contrast well with sand areas and more open areas - and having such contrast is important in an aquascape. Rocks with flat faces that are evenly lit by light will appear flat and unattractive in photographs. Diagonal lines drawn by rocks placed at an angle in an aquascape give a sense of movement and tension, whereas squarely placed rocks look stable and boring.

Smaller pieces should match the larger pieces somewhat for the aquascape to come together as a whole. This can be done by establishing a pattern that runs throughout the layout - for example, by tilting the rocks all at a similar angle, or using rocks with similar textures.

Example:This set of rocks look rather boring yes? The faces are all flat and unexciting. They look like a set of very uninteresting rocks, unbefitting for a refined Iwagumi aquascape.

The same set of rocks after they are tilted at an angle, after choosing the most aesthetic face for each rock. The slightly shadowed bottoms contrast nicely with the lighted textures up top. Tilting the rocks in a similar fashion brings unity to the three separate rocks.

Added another smaller rock (on the extreme left) to compliment the main rocks. Now the main rocks are united by similar angle tilt, and the smaller rocks echo the shape of the larger ones, bringing the structure together as a whole. Even smaller rock pieces are added to give a more natural transition in rock sizing and as a contrasting texture to both the sand and larger rock pieces.

Finer rock pieces are added at the base of the larger rocks to allow the entire rock structure to blend well into the substrate. Here we have a good naturalistic gradation in rock sizes from large to smaller pieces. Strong shadows contrast with both the sand and brighter rock faces.

Aquasoil or sand?

The area that is planted should be filled in with aquasoil and not sand. This allows us to substrate feed the carpeting plants nitrogen and phosphorus without dosing either nutrient into the water column. Minimizing nitrogen and phosphorus in the water column reduces green algae development on the rocks and allow us to maintain clean algae free rocks with less effort. If we used an inert substrate such as sand, we will need to dose more nutrients (specifically N and P) into the water column, and this encourages green algae development on the rocks.

Suitable carpeting plant species

Dwarf hair grass (Eleocharis acicularis, Eleocharis parvula)

Dwarf hair grass is a long time staple in the aquarium hobby. The plant grows as deep green strands that spread quickly through underground runners. Eleocharis acicularis grows more vertical and thus give a slightly taller carpet compared to Eleocharis parvula which has slightly shorter leaves that flop sideways. Both species are hardy plants that can tolerate poorer growth conditions compared to more sensitive species such as HC. 

The taller growth form of dwarf hair grass compared to more flat carpets such as MC and HC also allows them to hide the base of rocks more easily. This can smoothen the transition of rocks into the substrate layer.

Eleocharis acicularis carpet with Seiru rock.

Eleocharis parvula carpet, Seiryu rock aquascape - tank size 120x45x45cm.

MC (Micranthemum tweediei 'Monte carlo')

Monte carlo is a light green carpeting plant that has roundish leaves on a creeping green stem. It is hardier than the smaller sized HC, and has a moderate growth speed. It can even be grown without a substrate, by gluing it onto flat rock or wood surfaces. Monte carlo is the best candidate for non CO2 injected aquariums and together with dwarf hair grass, are the two easiest carpeting plants to grow. 

The light green tone of the Monte carlo foreground in this "dutch style" aquascape gives a nice contrast to the red stem plants in the back.

Monte carlo carpet, the larger leaved plant is Staurogyne repens.

HC (Hemianthus callitrichoides 'Cuba')

Hemianthus callitrichoides 'Cuba' or HC for short is one of the aquatic carpets with the smallest leaves. The light green carpet will spread quickly in good growth conditions. It requires adequate CO2 levels to grow in good form. Compared to Monte carlo, HC has thinner stems and is a much more delicate plant. It is much more difficult to grow well compared to Monte carlo or dwarf hair grass.

The small leaves of HC contrast well against the larger leaves of most other aquarium plants.

Neocaridina shrimp less than an inch long on HC carpet.

Monte carlo left top and HC bottom right. HC has smaller leaves.

Glosso (Glossostigma elatinoides)

Glossostigma elatinoides has round green leaves on an extended petiole. This plant spreads very quickly through runners when growth conditions are good. Each runner node usually produces a set of 2 or 3 leaves. Due to its high growth speed, this plant carpets even large tanks fast. It requires a bit more light compared to dwarf hair grass to grow well, and does best in CO2 injected aquariums.

UG (Utricularia gramminifolia)

Utricularia gramminifolia has short, light green leaves that are significantly broader compared to dwarf hair grass. UG is a bladder wort - a carnivorous plant that produces tiny bladder traps to capture microscopic prey. Similar to other carpeting plants on this page, the plant propagates in good speed through runners. These runners will tunnel through soil/aquasoil, but they will also attach to hardscape and other rough surfaces. UG can be grown easily on hardscape or floating if one does not want to use it on the substrate as a carpet.

Although Utricularia gramminifolia produces bladder traps, these traps are harmless to shrimp and fish. The plant does not need to be fed manually either, and unlike other carnivorous plants, UG can grow in fertile substrates and is not as sensitive to fertilizer. However, it does prefer to be planted in a biologically matured aquarium. Folks that plant it in fresh setups often find that it melts. Compared to the other carpeting options, UG can be harder to trim as it forms very dense mats quickly. The leaves are also more delicate and the plant requires a more stable tank to do well long term.

Strategy to avoid algae in an Iwagumi aquascape

1. Feed carpeting plants N and P from the substrate

Substrate feeding carpeting plants the macro elements Nitrogen and Phosphorous allows us to use water column fertilization without those 2 elements. In our Iwagumi tank examples above, we use APT 1 in the water column which contain all nutrients except N and P. Completely draining the water column of N and P minimizes algae growth on sand banks and hardscape.

2. Use low light levels

Many folks think of carpeting plants as plants that require high light levels to grow and spread but this is not true. Every carpet plant from Dwarf Hairgrass (Eleocharis acicularis/parvula), to HC (Hemianthus callitrichoides 'Cuba'), MC (Micranthemum tweediei 'Monte Carlo') can spread with as low as 20+ umols of PAR as long as CO2 injection is provided. We recommend substrate levels to measure between 30-60 umols of PAR but no more than that. This will keep algae to a minimum and keep white sand areas and rocks in their original color.

This 4ft Iwagumi has around 50 umols of PAR in the middle and 30+ umols of PAR at the sides. APT 1 is the only additive dosed into the water column for plant nutrient needs. 50-80% Weekly water changes.


This 2ft Iwagumi has around 40 umols of PAR at the center and 30+ umols of PAR at the edges. APT 1 is the only additive dosed into the water column for plant nutrient needs. 50-80% Weekly water changes.

3. Keep organic waste levels low

In planted tanks where there is a dominant amount of larger plants occupying most of ecological space, the tank becomes naturally algae resistant as higher level plants out-complete the algae. However, in Iwagumi setups, the amount of plant mass is small and we cannot depend on plant mass to defend the tank against algae.

Elevated organic waste levels can trigger algae even when light levels are already lowered. In lower light tanks, this can manifest as cyanobacteria (BGA) or diatoms (brown algae). In higher light tanks, it will manifest as GDA (green dust algae) on the glass and rocks. Keep organic waste levels low by having a lighter fish load if possible, and more water changes to keep water quality high. During water changes, siphoning away detritus on the substrate surface is important. Read here on how to water change the 2hr Way.

Iwagumi aquascapes that use too much light and/or have too high Nitrate/phosphate levels in the water tend to get green algae on the hardscape more easily. The carpeting plants will spread more quickly in a high light, high water column nutrient tank, however, this is at the expense of hardscape cleanliness. 

Putting a system together

Equipment list

Filter: Oase Biomaster 250

Light: Week aqua T90, hung 4 feet above tank and ran at 50% power

CO2: Injected through inline atomizer system, Aquatic farmer regulator

Fertilization: 2hr Aquarist APT 1, 1ml per day.

Substrate: 2hr Aquarist aquasoil, cosmetic sand

Rocks: Seiryu rock

Foreground plant: Eleocharis acicularis

Fauna: Pygmy cories, White cloud mountain minnows

Maintenance regime: 

Weekly water changes of 50-70%, where detritus on the substrate level is siphoned away, water change 2hr Way. Dwarf hair grass carpet trimmed every couple of months. Every 8 months or so, substrate will be enriched by APT Jazz root tabs. Oase pre-filter is cleaned every 3 weeks and the main chamber is serviced only once a year.

Other regular tasks include daily dosage of APT 1 water column fertilizer, at 1ml a day. CO2 system is checked regularly to make sure that CO2 levels remain optimal - Adequate CO2 (25-30ppm) allows the hair grass carpet to spread well even though low light levels are used.