Nobody has ever regretted ordering slightly too much stone. This is the arithmetic we use when quoting a build.
Hardscape stone
Dragon stone is light and hollow; seiryu and black mountain are dense. You price by weight but you should plan by eye — order the top of the range and expect to have two or three pieces left over.
| Tank | Dragon stone | Seiryu / Black mountain |
|---|---|---|
| 45 cm (45 × 30) | 4–5 kg | 5–7 kg |
| 60 cm (60 × 30) | 6–8 kg | 8–10 kg |
| 90 cm (90 × 45) | 12–15 kg | 15–18 kg |
| 120 cm (120 × 50) | 20–25 kg | 25–30 kg |
Soil and sand
The formula is simple: length (cm) × depth (cm) × layer (cm) ÷ 1000 = litres. A 60 × 30 cm footprint at 5 cm needs 9 litres — one bag. Build the bank higher at the back and you will use about 20% more.
Cosmetic sand is a 1–2 cm cap over that. A 5 kg bag covers roughly 60 × 30 cm.
Wood
One good piece beats three mediocre ones. For a 60 cm tank choose a branch about two-thirds the tank width (25–35 cm); for 90 cm, 40–50 cm; for 120 cm, 55–70 cm.
Plants
One tissue-culture cup plants roughly 20 × 10 cm of carpet at a 2 cm spacing. A full 60 cm carpet takes six to eight cups; a 90 cm takes twelve to fifteen.