SUBSTRATE & HARDSCAPE

Seiryu Stone

Angular grey-blue stone with white veining — the classic Iwagumi choice, but it hardens water.

Setup stage Substrate

Unplug before servicingHands out of the water firstDrip loop on every cableTest before you dose30 ppm CO₂ ceilingCycle before stocking

Substrate

Specification
Type	Metamorphic, calcite veins
Hardness	Hard, stackable
pH effect	Raises pH and KH over time
Colour	Grey-blue with white veins
Texture	Angular, sharp-edged
Preparation	Scrub, test in a bucket

Technical parameters
GH effect	Rises measurably over months
KH effect	Rises, buffering pH up
Soft-water suitability	Poor
Hard-water suitability	Excellent
Test method	Soak in a bucket, test GH weekly
Best style	Iwagumi, Nature

Seiryu stone is a metamorphic rock with sharp angular faces and white calcite veining. It is the traditional stone of the Iwagumi layout, where three or more stones are arranged as a mountain formation and the whole composition is the rock.

The reason it is not simply the default for every tank is its chemistry. Seiryu contains calcium carbonate, and it raises both GH and KH over time, which raises pH and can push a tank that was set up for soft-water fish or Caridina shrimp out of range. In a hard-water tank that is harmless; in a soft-water biotope it is a slow drift you will be fighting for the life of the scape.

Structurally it is much harder than Dragon stone and can be stacked with confidence. The sharp edges also mean it must be handled carefully and positioned so no livestock can wedge itself into a gap it cannot back out of.

Safety and welfare

Edges are sharp. Handle with gloves and check the tank for fish that could wedge into a crevice — a fish that goes in and cannot back out will die there.
Verify the effect on your water before you commit. Soak a piece in a bucket of tap water and test GH and KH weekly for three weeks.
Do not lean a tall stone against glass. If it shifts it will break the pane.

Using it well

In Iwagumi, one stone is the mountain, one is a supporting stone and one is a small stone leaning in the same direction. All three should share a bedding angle.

Sink the base of each stone well below the substrate line. A stone sitting on top of the substrate looks placed; a stone emerging from it looks grown.

If you keep soft-water fish, use Dragon stone instead. The pH drift from Seiryu is not something you can dose around indefinitely.

Best for

Iwagumi layoutsHard-water fishMonte Carlo carpetsNerite snail

Note. Parameters are conventional ranges across the category, not the claim of any one manufacturer. Nothing on this page is for sale and no outcome for any plant or animal is guaranteed. Simulator output elsewhere on this site is a simplified model, not a measurement — confirm everything with a test kit and the equipment's own instructions.

Seiryu Stone

Using it well

Best for

Works alongside