Why Seiryu Stone Raises KH

Written 2026-11-06

Seiryu stone is calcium-carbonate rock, so it keeps dissolving a little into the water, steadily raising KH (buffering capacity) and GH (hardness). Running a 24.3L nano tank with bee shrimp (crystal shrimp) substrate through the Water Kiwoogi simulator shows that without seiryu stone, KH stays in the 1–2 range and pH in the low 7s for all 60 days, and all 10 shrimp survive. Add three seiryu stones to the same tank and KH climbs to 9.97, GH to 14.72, by day 60 — shrimp start dying on day 16 and the colony is wiped out by day 43. Even a single stone leaves only 3 shrimp alive.

Why seiryu stone keeps pushing KH up

In this simulator, each seiryu stone dissolves 0.10 KH and 0.12 GH into the water per day (scaled to a 60L reference — the less water you have, the harder the same stones hit). Drop three seiryu stones into a fishless 60cm standard tank (59.4L) filled with tap water and KH climbs to 5.47 by day 10; put the same three stones in a 24.3L nano tank and KH reaches 7.19 by day 10 — nearly double the rise, since the tank holds less than half the water. The dissolving isn’t unlimited, though: as KH approaches 15 (the saturation point), the rate slows down and it doesn’t climb past that line.

That’s fatal for soft-water species like bee shrimp

Shrimp-specific soil pulls KH down hard to build the soft, slightly acidic water bee shrimp need — without any stone, this tank starts at KH 0.4, GH 4.4, pH 6.7. Bee shrimp need extremely soft water (GH 2–7, optimal 4; pH 5.5–6.9, optimal 6.3), and adding seiryu stone undoes exactly what the soil built. One stone alone pushes pH to 7.45 by day 10, and shrimp start dying from day 22 onward. Three stones push pH to 7.78 by day 10 and 7.89 by day 16 — deaths start right away on day 16, and all 10 shrimp are gone by day 43.

A non-calcium rock like sanmoku shifts KH and GH by only 0.01 a day, so it barely matters over 60 days — though even that small pull adds up enough over two months to nudge out 2 shrimp. That’s a tenth of seiryu’s daily rate (0.10 KH, 0.12 GH), and in a soft-water tank where you still want hardscape, that tenth is the difference between a thriving colony and a wipeout.

Choosing rock for your setup

If you want hardscape in a soft-water tank, non-calcium rock — sanmoku, lava rock, river pebbles — is the safer pick. On the other hand, for species that want harder water, like African cichlids, seiryu stone is a convenient way to raise KH and GH without extra dosing. If you’re worried about KH or GH after adding rock, test it directly, and if things look off, it’s safest to check with an aquarium shop or an expert.

The button below runs the exact tank from this guide — 24.3L nano tank (shrimp soil) with 3 seiryu stones and 10 bee shrimp. Try removing the stones or dropping to just one, and you’ll see KH stay far lower.

The numbers in this guide come from the Water Kiwoogi simulator model; real tanks can differ.