Aquascape Iwagumi Stones Glossary Guide: Oyaishi Soeishi Fukuseki
Iwagumi looks deceptively simple — a few stones, a carpet of grass, water — but every stone has a name, a position and a relationship to the others borrowed from centuries of Japanese garden design. The aquascape iwagumi stones glossary below names each role, explains the proportional relationships and shows how Singapore-based scapers apply the rules with locally available stone. This glossary entry on the aquascape iwagumi stones glossary from Gensou Aquascaping at 5 Everton Park is meant to take you from buying random rocks to setting up a competition-grade Iwagumi composition.
Definition in 50 Words
Iwagumi is a minimalist Japanese aquascaping style featuring an odd number of stones (typically 3, 5 or 7) arranged according to specific named roles, often atop a single carpet plant species. The composition follows asymmetrical balance, the golden ratio, and the Japanese garden principle that no two stones should match in size or character.
Oyaishi: The Main Stone
The Oyaishi is the largest, most visually dominant stone — the heart of the composition. It sits off-centre at roughly the golden ratio position (61.8 per cent from one side), tilted slightly to suggest natural settling. Oyaishi height should be approximately two-thirds of the tank’s water height. Choice of stone matters: Seiryu, Dragon Stone (Ohko), Yamaya and lava all work; the decoration and substrate range at Gensou stocks Seiryu and Yamaya in graded sizes.
Soeishi: The Supporting Stone
The Soeishi is the second-largest stone, placed adjacent to the Oyaishi to support it visually. It mirrors the Oyaishi’s lean and texture but at smaller scale — typically 60-70 per cent of the Oyaishi’s mass. The two together form the visual anchor of the composition. Distance between them should feel deliberate; touching stones look stacked rather than sculpted.
Fukuseki: The Third Stone
The Fukuseki balances the composition on the opposite side from the Oyaishi-Soeishi pair. Smaller than the Soeishi but still substantial — typically 30-40 per cent of Oyaishi mass. Its placement creates the asymmetric tension that makes Iwagumi visually engaging. Without a properly placed Fukuseki, three-stone Iwagumi compositions feel front-loaded and dead on the opposite side.
Suteishi: The Sacrificial Stones
Suteishi (literally “sacrificial stones”) are smaller scattered stones — usually two or three — placed to soften transitions between major elements and add ground-level interest. They look almost incidental but are deliberately positioned to direct the eye and balance negative space. Suteishi can be removed without destroying the composition; the main three-stone triangle still reads.
Golden Ratio Sizing
Classic Iwagumi sizing follows the golden ratio: Oyaishi at 1.0, Soeishi at 0.618, Fukuseki at 0.382. A 30 cm Oyaishi pairs with an 18 cm Soeishi and a 12 cm Fukuseki. This proportional system creates visual rhythm — the eye moves naturally from largest to smallest. Departures from the ratio require strong design intent; random sizing reads as amateur.
Stone Selection Criteria
All stones in an Iwagumi composition should come from the same family — never mix Seiryu with Dragon Stone in one scape. Look for asymmetrical character: a strong leaning angle, varied face textures, and a clear “best face” that defines orientation. Avoid stones that look symmetrical from multiple angles — they cannot anchor a directional composition.
Sankin: The Three-Stone Triangle
The classical Sankin arrangement places Oyaishi, Soeishi and Fukuseki at points of an asymmetric triangle, viewed from the front. Heights should differ; ideally none of the three should be equally spaced. Imagine the composition as a Buddhist triad — a central figure flanked by attendants. Sanzon is a related arrangement borrowed from Buddhist iconography for five-stone compositions.
Carpet Plant Pairing
Iwagumi traditionally uses a single carpet plant species to keep visual focus on the stones. Hemianthus callitrichoides “Cuba” (HC), Glossostigma elatinoides, Eleocharis acicularis “Mini” and Marsilea hirsuta are the four most-used species. Pick one and commit. Multiple species in an Iwagumi break the minimalist intent. The aquarium plants range stocks tissue-culture HC and dwarf hairgrass year-round.
Singapore Application
Tropical 28-30°C tank temperatures slightly limit carpet plant growth — HC prefers 22-26°C. A chiller from the chiller range set to 25°C produces tighter, denser carpets. PUB tap water at GH 2-4 suits HC and hairgrass directly without remineralisation. Pressurised CO2 from a quality regulator hitting 30 ppm during photoperiod is non-negotiable for competitive iwagumi growth rates.
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