Seiryu Stone pH: How Much KH It Adds and How to Use It
Updated November 2026
Seiryu stone raises pH because it contains calcium carbonate. The carbonate dissolves slowly into the water column, adds carbonate hardness, and that KH buffers pH upward. The effect is real, but it is also slow and controllable, and plenty of scapes run on seiryu with no trouble at all.
Whether it matters comes down entirely to what you keep.
- RaisesKH, GH and pH, slowly
- Skip it forCaridina and blackwater tanks
- Fine forNeocaridina, livebearers, African cichlids
- Measure withA GH and KH kit, weekly
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Seiryu stone KH drift estimator
Enter your tank and stone to see a band for how far KH may drift, and a weekly water change that holds it. It is an estimate, not a measurement.
What is actually happening in the tank
Seiryu sits in the limestone family, cut through with the pale calcite veins that give it its look. Those veins are the reactive part.
Calcium carbonate breaks down into calcium and bicarbonate ions. KH climbs, GH climbs with it, and pH follows because carbonate resists being acidified.
The softer and more acidic your source water, the faster it leaches. In already hard tap water the shift is often barely measurable.
Seiryu vs ryuoh, dragon stone, lava rock and slate
This table sorts five common hardscape stones by whether they hold carbonate. Where a source says nothing, the cell says so.
| Stone | Reacts to acid | Effect on KH and GH | Fits which tanks | Source |
|---|---|---|---|---|
| Seiryu stone | Yes, it is calcium carbonate | Raises KH, GH and pH | Hard or neutral water: neocaridina, livebearers, African cichlids | Aquarium Science rocks article |
| Ryuoh stone | Not stated by the maker | ADA: may raise pH and hardness slightly | Test KH first; not stated for soft water | ADA product text |
| Dragon stone | Not tested here | No source we read gives a carbonate figure | Run the acid test on your own piece before using it in soft water | None found; Aquarium Science covers rocks in general |
| Lava rock | Not tested here | Aluminosilicate rock; carbonate lava is very rare | Soft-water tanks; rinse dust off first | Aquarium Science rocks article, lava rock myths |
| Slate | Not tested here | No source we read gives a carbonate figure | Run the acid test on your own piece before using it in soft water | None found; Aquarium Science covers rocks in general |
Sources read on 1 November 2026: the Aquarium Science rocks article and ADA product text for Ryuoh stone. Reaction in a test is a sign of calcium carbonate. It is not a measured KH figure, so test your own water.
The acid test at home
At home, put a drop of household vinegar on a dry piece and watch closely. Visible fizzing means carbonate.
Vinegar is a weak acid, so a rock that holds carbonate may show only a few fine bubbles. A quiet result with vinegar does not prove a rock is inert, so use the stone comparison above as well.
Seiryu fizzes. So do limestone, marble, shells and coral. Our guide to safe and unsafe rocks sorts what reacts from what stays inert.
Who should skip it
Caridina shrimp are the clear no. Crystal reds and taiwan bees want soft, low-KH water with a remineralized GH target, and seiryu works against that setup every day. Caridina vs neocaridina lays out which species tolerates what.
Blackwater tanks are the other mismatch, since the whole point is a low pH driven by tannins and carbonate cancels that out.
Wild-caught soft water fish belong in the same column.
Who can use it freely
Neocaridina shrimp, most livebearers, African cichlids, and hard water community fish either do fine or actively prefer the harder water.
Ordinary planted tanks on tap water are usually fine too, especially with regular water changes diluting the buildup.
Test KH before you add the stone and again a month later, using GH and KH for planted tanks as your reference for target ranges.
Keeping the effect small
Use less stone. Two or three focal pieces move your parameters far less than a full iwagumi wall does.
Prefer larger single pieces over many small ones, since exposed surface area drives the dissolution rate.
Some keepers seal the stone with an aquarium-safe clear coat. It hides the veins that give seiryu its look and can chip, so treat it as a partial measure.
Bigger water changes with soft or RO-blended water hold the line if you want the look and the low numbers. The estimator above turns your tank size and ceiling into a weekly percentage, and weekly tests for the first month show your actual rate rather than a guess.
How we sourced these figures
The rock facts come from the Aquarium Science rocks and wood articles, and ADA product text for Ryuoh stone. Product details come from the Amazon listings, read on 1 November 2026.
The KH estimator is our own model with the assumptions printed beside it. We did not run tank tests, and no figure on this page is a measurement from our own water.
Frequently asked questions
How much does seiryu stone raise pH?
There is no fixed number, because it depends on how much stone you use, how soft your source water is, and your water change routine. Soft water tanks with heavy hardscape see the largest shift, while hard tap water tanks often change very little. Test KH before and after to get your own figure.
Can you use seiryu stone with shrimp?
With neocaridina, yes, and the added hardness is generally helpful for shelling. With caridina it is a poor match, since those species are kept at low KH and seiryu pushes constantly against that. Choose a non-reactive rock instead if caridina are the plan.
Does boiling seiryu stone stop it raising pH?
No. Boiling or soaking cleans the surface and removes dust, but it does not remove the calcium carbonate that makes up the rock. The only real controls are using less stone, sealing it, or diluting with larger water changes.
Is the vinegar test enough to check a rock?
Vinegar is a weak acid, so a rock that holds calcium carbonate may only show a few fine bubbles. Aquarium Science says a stronger acid shows the reaction clearly. A fizz means carbonate, but a quiet result with vinegar does not prove the rock is inert.
Which rocks do not raise KH in soft water?
We found no source giving a carbonate figure for slate or dragon stone, so run the acid test on your own pieces before using them in soft water. Aquarium Science describes lava rock as an aluminosilicate rock, and carbonate lava as very rare. Ryuoh is different: ADA says it may raise pH and hardness slightly.
