Category: Hardscape

Aquarium driftwood comes in two broad kinds: light, branching woods such as spider wood and manzanita that float at first, and dense woods such as mopani that sink straight away. Any of them can tint the water and grow a harmless white film. Light wood sinks once it has soaked up enough water.

The main types

These are the woods most often sold for aquascaping, and what the sources say about each.

Wood	Look	Sinks?	Source
Spider wood	Pale, fine branching roots	Floats at first	Our spider wood page
Manzanita	Branching shrub wood from western North America	After about 4 to 7 days’ soaking	Tannin Aquatics
Talawa	Branchy but straight-lined; two-tone from sandblasting	Floats at first	Aquasabi
Moorwood (bog wood)	Dark brown, smooth, often slightly shiny	Floats if bought dry, sinks if bought wet	Aquasabi
Mopani	Gnarled, two-tone, little branching	Usually straight away	Aquasabi
Mekong	Straight and narrow, with deep furrows	Straight away	Aquasabi
Malaysian	Dark brown and craggy	Usually straight away (sellers differ)	Buce Plant, Tannin Aquatics

Aquasabi’s advice for any layout is to stick to one kind: it says a single wood type looks much more harmonious. The light, branching woods suit fine detail, and Terrarium Tribe suggests saving the heavy woods such as mopani for the centrepiece.

Malaysian driftwood

Malaysian driftwood is the classic dark aquarium wood, rich brown and craggy. Terrarium Tribe describes it as dark hardwood from “a variety of trees all native to Malaysia”. No reliable source names the species, so treat any listing that does with caution.

Most sellers, including Buce Plant and Bulk Reef Supply, call it dense and say it usually sinks without a pre-soak. Tannin Aquatics sells a lighter, porous grade that needs soaking to sink, so check the description of the piece you buy. Expect tannins: Tannin Aquatics calls it “loaded with tannins”. Terrarium Tribe rates it the only wood that comes close to mopani for toughness.

How to prepare driftwood

• Rinse and scrub with a soft brush to remove dirt and debris, as Tannin Aquatics suggests. Don’t use bleach: Aquarium Science warns it can stay in the wood in a form water conditioner can’t neutralise.
• Soak it in a separate container. Aquasabi’s classic method is a few weeks in water, changed from time to time, in an open container so gas can escape. Tannin Aquatics says there is no real shortcut: the wood has to waterlog to sink.
• Or soak it in the tank. Aquasabi suggests weighting it down, wedging it between stones, or fixing it with glue, silicone or cable ties. ADA’s advice is a stone on top for about a week.
• Check every piece. Aquasabi says to make sure each piece stays down before you use it in a layout, or a floating root can wreck the scape when you fill the tank.

Dense woods such as mopani and Mekong can skip most of the soak, though a pre-soak still draws out some of the tannins.

Should you boil driftwood?

The sources disagree more on this than on anything else about wood.

Source	View on boiling
Buce Plant (shop)	Boil 1 to 2 hours to help release tannins
LiveAquaria (shop)	Boiling 1 to 2 hours first may shorten the soak to 48 to 72 hours
Tannin Aquatics	Speeds manzanita up by a day or two at most; hardly worth the trouble
ADA	Even boiling can’t get the tannins out completely
Aquasabi	Never boil or scald moorwood, which may rot later
Aquarium Science	Don’t boil wood: it only reaches surface tannins, softens the wood, invites water mold and doesn’t make wood sink

Soaking does everything boiling claims to, more slowly and without the risks. Skip the pot unless the piece is small and you’re short of time, and never boil moorwood. Aquarium Science also warns against baking wood in an oven, which is a fire risk.

Brown water from tannins

Driftwood releases tannins and other humic substances that tint the water tea-brown, and Aquasabi says the denser woods are the most likely to do it. It is harmless. ADA says the amount that leaches naturally does no harm to the tank’s life, and Aquarium Science says tannic acid lowers pH only very slightly, from about 7.4 to 7.3.

If you’d rather have clear water, ADA says repeated water changes clear it gradually, and Aquarium Science says activated carbon and tannin-removing resin media both absorb it. Don’t expect it to stop for good: Aquarium Science says wood that releases tannin will do so for years. Some keepers want the tint, and a blackwater biotope is built around it.

The white fuzz on new wood

A white, slimy or cottony film often grows on new driftwood in its first weeks. The sources can’t agree what it is: Aquasabi says bacteria, ADA and Tannin Aquatics call it a fungus, and Aquarium Science says it is water mold. They all agree it is harmless and temporary.

Aquasabi says it feeds on sugars left in the wood and vanishes once they are used up, and that snails, shrimp and some fish eat it. You can siphon it off or brush it away. Aquarium Science says it typically lasts four or five weeks and won’t spread to fish. Its one warning: if the mold persists, the wood smells bad or starts to fall apart, the wood is too soft and should come out.

Can you use wood you found yourself?

Aquarium Science says yes, with care. Its test is to smell the wood: dead wood, wet or dry, with no smell of sap or chemicals is fine, while fresh pine, fresh cedar and strongly scented eucalyptus are not. It also says to smell shop-bought wood, because some suppliers oil it and the oil has killed fish. Tannin Aquatics takes the cautious line: the wood must be dry with no live wood or sap, and it is better to buy from sellers of aquarium-safe wood.

Aquarium Science also dismisses the idea that only hardwoods are safe, saying a wood’s hardness has little to do with how long it lasts. Wood from a stream can carry hydra or planaria, which it says matters mainly in shrimp tanks.

Planting on driftwood

Aquasabi says most epiphytes grow onto wood over time: mosses, ferns, Anubias and Bucephalandra. Moss is also useful for hiding a cut edge or an awkward spot, and both Java moss and Java fern attach this way. Porous lava rock beside the wood gives the same plants another surface, and Aquasabi says black lava works very well with driftwood.

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Aquarium driftwood questions

How long does driftwood take to sink?

It depends on the wood. Dense woods such as mopani and Mekong sink straight away. Light woods need to waterlog: Tannin Aquatics says manzanita takes about 4 to 7 days, and Aquasabi’s classic soak runs to a few weeks.

Should you boil driftwood before putting it in an aquarium?

Sources disagree. Shops recommend 1 to 2 hours to release tannins, while Aquarium Science says boiling softens wood and doesn’t help it sink, and Aquasabi says never to boil moorwood. Soaking is the safer route.

Is the white fuzz on driftwood harmful?

No. Aquasabi, ADA, Tannin Aquatics and Aquarium Science all call it harmless and temporary, though they disagree on whether it is bacteria, fungus or water mold. Snails and shrimp eat it, and it usually clears within weeks.

Sources: Aquasabi, Preparing driftwood; Aquasabi, Types of hardscape; Aquasabi, Driftwood in a tank with invertebrates; ADA, Hardscape materials (via Aquasabi); Aquarium Science, Wood; Aquarium Science, Water mold; Tannin Aquatics, A few notes on wood in the aquarium; Tannin Aquatics, ‘Wood’ you? Well, yes, I will; Tannin Aquatics, ‘Wood’ you believe this; Tannin Aquatics, Manzanita; Terrarium Tribe, Wood for terrariums; Terrarium Tribe, Mopani wood guide; Buce Plant, Malaysian Driftwood (shop listing); Bulk Reef Supply, Malaysian Driftwood (shop listing); LiveAquaria, Malaysian Driftwood (shop listing); Tannin Aquatics, Malaysian Driftwood (shop listing).

Lava rock is light, porous volcanic stone, sold in black, red and dark brown grades for aquascaping. Its pores give plant roots a grip, which makes it a favourite base for mosses and ferns. Aquasabi classes it as water-neutral, though ADA rates its own KUMU lava stones as having a moderate effect on hardness.

What lava rock is

Aquasabi describes it as stone of volcanic origin with a porous texture that makes it very light. Aquarium Science puts it more bluntly: “Lava rock is just a porous natural ceramic product.”

The light weight is the practical draw. Aquasabi says porous stones such as lava give more volume per kilo than dense stones, so large structures are possible, and you need considerably less of it by weight than of a heavy stone. Its rule of thumb for stone in general is your tank’s volume in litres divided by six, in kilograms. With lava you can come in under that.

Does lava rock float?

Sometimes, briefly. Aquasabi reports that some of its Island Lava floated on the surface for a short while before sinking, and Buce Plant, which sells lava, says smaller pieces may be slightly buoyant. Aquarium Science says it doesn’t float. Drop each piece in water before you build, and weight or wedge any that bob up.

Does it change your water?

Mostly no, with one exception worth knowing about.

Source	What it says
Aquasabi guide	Lava doesn’t influence water quality; it lists Black Lava among its water-neutral stones
Aquasabi and Buce Plant listings	Black, red and Icelandic lava are inert and don’t raise hardness
ADA KUMU lava (Aquasabi listing)	Black: moderate effect on GH and pH. Red: low effect on pH, moderate on GH

So the ADA claim covers one product line, and Aquasabi’s own guide still calls lava neutral. If soft water matters to you, for shrimp or soft-water plants, soak-test the stone you actually buy. Our aquascaping rocks page explains how.

Is it good filter media?

The shops say yes and the one test says no. Buce Plant’s listing claims its millions of tiny holes give beneficial bacteria a huge surface, and ADA’s listing credits it with natural biofiltration. Aquarium Science tested half-inch lava rock and found it did poorly at oxidising ammonia, which it says surprised it, and it lists “lava rock is a great biological filtration media” among hobby myths. It also says garden-centre lava, typically two to three inches across, is far too big to work as filter media.

Buy lava for the look and for planting. Treat any filtration benefit as unproven.

The colours on sale

Grade	How sellers describe it
Black lava	Very dark, black to grey (Aquasabi, Buce Plant)
Red lava	Deep brick red to burnt orange (Buce Plant)
Icelandic lava	Deep, dark brown when submerged (Buce Plant)
Galapagos rock	Dark, with some brown accents (Aquasabi)

All of it looks darker wet, Buce Plant notes. Aquasabi says a classic Iwagumi can be built from black lava, whose dark colour contrasts with the grey stones more commonly used.

Planting on lava rock

This is lava’s real strength. Aquasabi calls the porous structure ideal for ferns and mosses, and describes “Green Reef” scapes: tall lava structures covered in epiphytes such as Microsorum and Bolbitis ferns and moss, whose roots find a grip in the pores. It adds that lava is often used with driftwood roots, the stones covered in moss for forest-style scapes.

Tropica grows plants on lava for sale, including Anubias, Bucephalandra, Cryptocoryne, Microsorum (Java fern) and Bogor moss. It says plants grown directly on wood and stone are far hardier than plants grown in pots.

Preparing it

Rinse every piece under running water. Aquasabi says this removes fine dust that would otherwise cloud a new tank, and its listing for WIO red lava adds that fine mechanical filtration may be needed for 24 to 48 hours. Don’t use cleaning agents. Aquarium Science sees no point in boiling or bleaching rock, since a new fish or plant brings in far more pathogens than any stone. If the water does cloud, our cloudy water page covers the causes.

Lava breaks easily. Aquasabi says black lava crushes readily with a hammer and chisel, and to cover the stone with a cloth first so the shards don’t hurt anyone.

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Lava rock questions

Does lava rock raise pH or hardness?

Aquasabi says lava doesn’t influence water quality, and most sellers call it inert. The exception is ADA’s KUMU lava, which ADA rates as having a moderate effect on GH. Soak-test it if soft water matters to you.

Does lava rock float in an aquarium?

Occasionally, for a short while. Aquasabi saw some Island Lava float before sinking, and Buce Plant says small pieces may be slightly buoyant. Test each piece before you build.

Is lava rock sharp enough to hurt fish?

Aquarium Science says no. It says the edges of lava rock used in aquariums are far too dull to cut a fish, and that the rare glassy lava sharp enough to cut skin is only found near fresh eruptions.

Sources: Aquasabi, Types of hardscape; Aquasabi, Choose your hardscape by weight; Aquasabi, Black Lava (shop listing); Aquasabi, ADA KUMU Black Lava Stone (shop listing); Aquasabi, ADA KUMU Red Lava Stone (shop listing); Aquasabi, WIO Wild Red Lava Stone (shop listing); Buce Plant, Black Lava Rock (shop listing); Buce Plant, Red Lava Rock (shop listing); Buce Plant, Icelandic Lava Stone (shop listing); Tropica, AquaDecor; Aquarium Science, Lava rock; Aquarium Science, Rocks; Aquarium Science, Falsehoods and myths.

Mopani wood is a dense, two-tone African hardwood that sinks almost straight away and lasts for years underwater. The catch is tannin: most sources say it stains water brown more than most aquarium woods, though Aquasabi says only slightly. Soaking it for a week or two before use takes the worst out.

What mopani is

Mopani comes from the mopane tree, Colophospermum mopane, which the Wood Database, a timber reference, places in southern Africa. Tannin Aquatics lists its range as South Africa, Zimbabwe, Mozambique, Botswana, Zambia, Namibia, Angola and Malawi, and says the tree occurs only in Africa, in hot, dry places on alkaline soils. Aquasabi and Terrarium Tribe both describe the aquarium pieces as root wood.

It is very hard. The Wood Database calls mopane difficult to work, “mainly on account of its incredibly high density”, and Aquasabi classes it as a hardwood.

The two-tone look

Most pieces are two colours: Aquasabi describes yellow and brown, and Buce Plant, which also sells it, sandy tan and deep chocolate brown. Aquasabi says the two-coloured wood is partly sandblasted. The shape is gnarled and knotty, with little branching, which Tannin Aquatics says is the appeal: the texture and colour, more than the outline.

That makes it a centrepiece wood. Terrarium Tribe puts it this way: use mopani’s weight for the centrepiece and leave the fine accents to lighter woods such as spider wood and manzanita.

It sinks, usually

Mopani’s density is the reason people buy it. Aquasabi calls it “instantly-sinking”, Buce Plant says it typically sinks immediately, and Terrarium Tribe says soaking it to make it sink is rarely necessary. Aquasabi’s own listing adds a caveat: its pieces aren’t pre-soaked, so the time to sink can vary. Check each piece stays down before you build around it.

How much it stains the water

This is where the sources split.

Source	What it says about mopani’s tannins
Aquasabi	Can stain the water slightly at first
Buce Plant	Very rich in tannins, giving a dark tea-coloured tint
Tannin Aquatics	Releases a lot, during curing and beyond. A roughly 10-inch piece browned a 20-gallon tank in a couple of days, even after a two-day soak
Terrarium Tribe	As far as driftwoods go, one of the worst for it

The weight of opinion says to expect a noticeable tint. It is harmless: Terrarium Tribe calls the tint non-toxic, and Aquarium Science, writing about wood tannins in general, says they lower pH only very slightly, from about 7.4 to 7.3. Tannin Aquatics also warns that mopani keeps leaching for a long time, so a pre-soak reduces the tint rather than ending it.

How to prepare mopani

• Rinse and scrub. Tannin Aquatics suggests a good rinse and a light scrub with a soft brush to remove debris.
• Soak it. Tannin Aquatics soaks mopani for a week or two to draw out the first burst of tannins, and changes the soak water every few days.
• Clear what’s left. Small water changes plus activated carbon or a tannin-removing filter medium clear the water within a few days in most cases, according to Tannin Aquatics.

Boiling is the shortcut people ask about, and the sources disagree. Buce Plant recommends 1 to 2 hours for clear water. Terrarium Tribe reports people doing several 2 to 3 hour boils and still finding it leaching, and Tannin Aquatics prefers to soak and wait. Aquarium Science advises against boiling any wood, saying it only reaches the surface tannins and softens the wood. Our aquarium driftwood guide sets out the whole boiling debate.

Is it safe for shrimp?

Yes, according to Aquasabi. Mopani picked up a reputation for killing shrimp, and Aquasabi traced it to the sandblasting: some suppliers used blasting media unsuitable for invertebrates, and tiny metal fragments were found in the crevices. It says manufacturers now cater for shrimp keepers and that “it’s safe to say that Mopani is shrimp-proof”.

Two smaller points. Aquasabi says a bacterial film can appear on new mopani, and Tannin Aquatics says it occasionally gets a surface fungus, dealt with the same way as on manzanita. And plecos may pick at mopani, but Tannin Aquatics says they would rather chew something softer.

How long it lasts

Years. Tannin Aquatics says it lasts “years and years” in an aquarium, and Buce Plant says it breaks down much more slowly than other woods. As timber, the Wood Database rates mopane very durable and resistant to termites.

Tannin Aquatics raises one concern: mopane is a commercial timber used for flooring and furniture, and there is concern about how sustainably it is harvested. The Wood Database notes that the species isn’t listed by CITES or on the IUCN Red List.

Planting on mopani

The knots and crevices hold epiphytes well. Aquasabi suggests moss or ferns, and Buce Plant calls it a long-lasting base for both. Tie or glue Java fern, Anubias, Bucephalandra or Java moss into the gaps and let them take hold.

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Mopani wood questions

Does mopani wood sink?

Usually straight away. Aquasabi calls it instantly sinking and Buce Plant says it typically sinks on arrival, because it is so dense. Aquasabi adds that its pieces aren’t pre-soaked, so the odd one may take longer.

How long should you soak mopani wood?

Tannin Aquatics suggests a week or two in fresh water, changing it every few days, to draw out the first burst of tannins. Expect some tint afterwards: it keeps leaching for a long time.

Is mopani wood safe for shrimp?

Aquasabi says yes. Old reports of shrimp deaths came from unsuitable sandblasting media leaving metal fragments in the wood, and it says manufacturers have long since fixed that.

Sources: Aquasabi, Driftwood in a tank with invertebrates; Aquasabi, Mopani Wood (shop listing); Tannin Aquatics, ‘Wood’ you believe this; Tannin Aquatics, ‘Wood’ you? Well, yes, I will; Terrarium Tribe, Mopani wood guide; Buce Plant, Mopani Wood (shop listing); The Wood Database, Mopane; Aquarium Science, Wood.

Dragon stone and Seiryu stone are the two rocks most aquascapes are built from, and your water makes the choice. Dragon stone is inert. Seiryu is limestone-based and may harden the water a bit, more so in a tank running CO2. The looks split just as clearly: warm, pitted clay against sharp grey peaks.

Side by side

	Dragon stone (Ohko)	Seiryu stone
Made of	Clay-based sedimentary rock	Limestone-based rock
Effect on water	Water-neutral	May harden the water a bit
Surface	Pitted, full of holes and crevices	Sharp and angular, pale veins in grey
Handling	Crushes into fragments quite easily	Compact, but workable with hammer and chisel
Suits	Soft water, shrimp, cave-like texture	Hard-water fish, mountain-style layouts

Water is the difference that matters

Aquasabi classes dragon stone as water-neutral, and Buce Plant says it is inert and will not influence water parameters. Seiryu is the opposite case. Aquasabi says it contains a little lime and may harden the water a bit, and Horizon Aquatics says it may slightly raise pH, KH and GH.

CO2 injection makes the gap wider. In Aquasabi’s article with aquascaper Oliver Knott, calcareous stones tend to harden the water far more when a CO2 system is running, because the carbonic acid dissolves the lime. The remedy he gives is regular, large water changes with soft water.

So the rule is simple. For soft-water fish, shrimp or a high-tech tank, dragon stone removes a variable. Seiryu suits hard-water livestock, or a keeper happy to manage a slow rise in hardness.

Look and layout

Seiryu’s jagged grey rock reads as a mountain range at tank scale, which is why it became the classic stone of the Iwagumi layout. Dragon stone’s holes and overhangs read as caves instead, and its crevices hold moss and small epiphytes, which suits a Nature Aquarium.

Whichever you pick, use one. Aquasabi warns that if you use various types of stone, the whole picture will lose its harmonious effect.

Handling and preparation

Dragon stone is the easier rock to shape and the harder one to clean. Aquasabi says it can be crushed into fragments quite easily, and Buce Plant says it breaks into smaller pieces with a chisel and hammer, though it is relatively brittle. It also holds loam in its crevices, which Aquasabi says to remove with a sharp object before a thorough rinse.

Seiryu is harder to break. Aquasabi calls it quite a compact stone, though still workable with hammer and chisel, and Terrarium Tribe describes it as extremely hard and heavy. On weight, Aquasabi’s bulk-weight table puts the two rocks in the same group, so the same size of layout takes about the same kilos of either.

Not sure which you have?

Looks can mislead. Horizon Aquatics says dark Seiryu is ordinary Seiryu that has been acid-washed, and it looks nothing like the pale original. An acid test settles it: carbonate rock fizzes and clay rock does not. The aquascaping rocks guide covers that test and the two-week soak test that confirms it.

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Dragon stone vs Seiryu stone questions

Which is better for shrimp, dragon stone or Seiryu stone?

Dragon stone. It is inert, so it leaves the water stable, while Seiryu may slightly raise pH, KH and GH. Shrimp tanks are where a water-neutral rock does the most good.

Can you mix dragon stone and Seiryu stone?

You can, but Aquasabi advises against it on looks alone: mixing types of stone costs a layout its harmonious effect. Pick one and use it throughout.

Does dragon stone raise pH like Seiryu?

No. Dragon stone is clay-based and water-neutral. Seiryu is the one that may nudge pH, KH and GH upwards, and more so in a CO2-injected tank.

Sources: Aquasabi, Types of hardscape; Aquasabi, Oliver Knott on water-hardening stones; Buce Plant, Dragon Stone (Ohko); Aquasabi, Choose your hardscape by weight; Horizon Aquatics, Dark Seiryu stone vs Seiryu stone; Terrarium Tribe, Seiryu stone hardscape guide.

Dragon stone, also sold as Ohko stone, is the pitted, clay-based rock in warm earthen browns that turns up in a huge number of planted aquariums. It is inert, so unlike Seiryu stone it will not push your water hardness around, and it breaks to size easily with a hammer and chisel.

Ohko stone and dragon stone are the same rock

The two names cause more confusion than the rock deserves. Aquasabi lists it as dragon stone with Ohko stone as the alternative name, and Buce Plant sells it as Dragon Stone (Ohko). Same rock, two shop labels, and the spelling “Okho” you will also see is simply a common slip.

What dragon stone looks like

Tan to reddish brown, deeply pitted, and full of hollows and crevices. The name comes from that scale-like surface. Those pockets are the reason people reach for it. They hold moss and small epiphytes, they read as caves and overhangs at aquarium scale, and they catch light in a way flat rock does not.

Is dragon stone inert?

Yes. Dragon stone is an argillaceous rock, meaning clay-based, and it does not influence water hardness. Aquasabi classes it as water-neutral, and Buce Plant describes it as inert. It sits with lava rock in the water-neutral group, which makes it the straightforward choice for soft-water scapes and shrimp tanks, where stable parameters do more for you than any particular rock shape.

That is the practical difference between dragon stone and Seiryu, its usual alternative. Seiryu is limestone-based and slowly hardens the water. Dragon stone does not. If you are unsure which you have, the aquascaping rocks guide covers the acid and soak tests that tell them apart.

Dragon stone compared with Seiryu stone

	Dragon stone (Ohko)	Seiryu stone
Effect on water	Water-neutral, does not influence hardness	Limestone-based, may harden the water a bit
Surface	Pitted and holey, full of crevices	Sharp and angular, pale veins through grey
Handling	Crushes into fragments quite easily	Compact, but workable with hammer and chisel
Suits	Soft-water scapes, shrimp, cave-like texture	Hard-water fish, mountain-style layouts

The water and handling rows come from Aquasabi, and the reason to care is in the first row. A CO2-injected tank dissolves lime faster, so a lime-bearing rock pushes hardness up more in a high-tech setup than in a low-tech one.

Brittle and easy to break

Buce Plant says its clay-like make-up leaves it relatively brittle compared with other stones, and Aquasabi says it can be crushed into fragments quite easily. That cuts both ways. A hammer and chisel will break a large piece into smaller ones when a layout needs them, but careless handling can also break a piece you wanted whole.

Don’t expect it to be light, though. Aquasabi’s table of stones by bulk weight puts dragon stone in the same group as Seiryu, so the same size of layout takes about the same weight of either.

Where does dragon stone come from?

Retail listings are vague on this. Aquasabi and Buce Plant give no source country on their pages, and we haven’t found a reliable source that does, so treat any origin a listing gives with caution. What Aquasabi does give is the rock type: argillaceous, meaning clay-based.

How to prepare dragon stone

Dragon stone is notorious for holding loam deposits in its nooks and crannies, so cleaning is most of the job. Skip it and a new dragon stone aquarium starts life with that loam in the water.

• Soak: start with the stones in a bucket of cold water.
• Pick out the loam: work it out of the crevices with something thin and sharp. Aquasabi suggests a sharp object.
• Rinse: rinse each stone thoroughly. Aquasabi says to remove all clay residues this way, and Buce Plant says rinsing removes natural dust and sediment.

Do all of this before the stone goes into the scape, while every crevice is still easy to reach.

Planting on it

The texture suits epiphytes, which attach to surfaces rather than rooting in substrate. Anubias, Java fern, and Java moss all take to it, and the crevices give you somewhere to wedge a rhizome while it attaches. Just keep the rhizome above the surface rather than buried.

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Dragon stone questions

Does dragon stone affect pH or water hardness?

No. It is an inert, clay-based rock that does not influence water hardness, which is what makes it a safe default for soft-water tanks and shrimp.

Do you need to boil dragon stone?

None of the sources behind this page call for boiling it. What they all stress is cleaning: pick the loam out of the crevices and rinse the stone thoroughly before it goes in.

Dragon stone or Seiryu stone?

Dragon stone if you want a knobbly, cave-like rock with no effect on water chemistry that breaks to size easily. Seiryu if you want compact, mountainous grey rock and you are comfortable managing a slow rise in hardness. Use one or the other throughout a scape rather than mixing them.

Sources: Aquasabi, Types of hardscape; Buce Plant, Dragon Stone (Ohko); Aquasabi, Choose your hardscape by weight; Aquasabi, Ohko Dragon Stone (shop listing); Aquarium Science, Rocks.

Seiryu stone is the rugged grey rock, often shot through with white veins, that defines the classic Japanese aquascape and the Iwagumi layout in particular. It is limestone-based, so the one thing to know before buying it is that it will harden your water slightly.

What Seiryu stone looks like

Sharp, angular grey rock with deep crevices and pale veins running through it. Aquasabi calls it quite a compact stone, though still workable with hammer and chisel, where dragon stone crushes into fragments quite easily. Those jagged edges are why it reads as a mountain range in miniature, and why it became the default choice for the stone-led layouts Takashi Amano popularised. Buce Plant, which sells it, notes that the colour deepens when wet.

Seiryu, Ryuoh and dark Seiryu

The names cause more confusion than the rock. Most shops sell Seiryu and Ryuoh as one stone: Aquasabi lists “Ryuoh or Seiryu”, and Horizon Aquatics sells Seiryu “also known as ryuoh”. ADA, though, sells Ryuoh under its own name, and Terrarium Tribe reports that some in the trade believe the Seiryu sold outside Japan is really Ryuoh, a duller grey stone with fewer white veins. In the tank they behave alike: Aquasabi and ADA both say Ryuoh hardens the water. You may also see the names Seiryu-Seki and Mini Landscape Rock.

Dark Seiryu is sold as a darker form of the same stone. Horizon Aquatics says it is natural Seiryu put through an acid wash, which dulls the bright calcite veins to leave a charcoal or slate-grey stone with the same sharp structure. Not every source agrees on how it is made: Aquasabi and Buce Plant describe their dark versions by colour alone, and Terrarium Tribe says it couldn’t find what black Seiryu is or where it comes from. Either way, Horizon and Buce Plant say the dark stone still raises pH and hardness slightly, so choosing it for the colour won’t get you a softer-water rock.

It hardens your water

This is the part that catches people out. Seiryu contains a little lime, and Aquasabi says it may harden the water a bit. Horizon Aquatics says the same of both standard and dark Seiryu: either may slightly raise pH, KH, and GH. In a low-tech tank, that is a small effect.

There is also a ceiling. Aquarium Science says calcium carbonate, Seiryu included, dissolves only enough to bring water to about pH 7.6 to 7.9, no higher. It calls that a fine pH for adult fish, though a few blackwater species won’t spawn in it. Both hardness readings rise because of how the lime dissolves: Knott explains that it releases calcium, which raises GH, and carbonates, which raise KH. ADA adds that a lot of white on a stone doesn’t mean a bigger rise.

CO2 injection changes the picture. The carbonic acid it produces dissolves the lime in the stone, which raises carbonate and total hardness further. In Aquasabi’s article with aquascaper Oliver Knott, calcareous stones “tend to significantly harden the water if a CO2 system is used”, while the influence may be smaller without it. ADA agrees, and says the rise is particularly marked with Ryuoh. Horizon Aquatics takes the opposite view, that the effect is usually minimal in planted tanks with CO2 and regular water changes.

The standard counter is changing larger amounts of water frequently. Aquasabi recommends refilling with demineralised or reverse-osmosis water, and Knott adds that active soil helps pull minerals back out of the water. Aquasabi’s Seiryu listing puts the routine at about 50% of the water each week.

Preparing and placing it

Rinse it well under running water before it goes in. Aquasabi says this removes the fine dust that would otherwise cloud a new tank. There’s no need to boil or bleach it: Aquarium Science says rocks are fine as they are, even ones that fizz in acid.

Seiryu is compact and hard to break. Aquasabi says it can still be worked with hammer and chisel, while Terrarium Tribe finds it extremely hard to break and advises buying the sizes you need. Terrarium Tribe also warns that a falling piece can crack the glass, so it suits upright stones better than stacks or caves. Its advice is to anchor each stone by burying its base slightly and packing substrate around it.

For how much to buy, Aquasabi’s rule of thumb is your tank’s volume in litres divided by six, in kilograms. Seiryu needs no adjustment to that figure, where lighter lava would need less.

Using it in an Iwagumi

Seiryu is one of the stones Aquasabi names for an Iwagumi, a layout built from a single type of stone with no wood. Its guidance is to use an odd number of stones in different sizes: one large main stone (Oyaishi), a smaller secondary stone (Fukuishi) as its counterpoint, and small supporting stones (Soeishi and Suteishi). Let the lines in the stone’s texture guide where each one goes.

ADA’s advice for Ryuoh is to follow the ridge line and keep the stones looking continuous, and to have plenty of sizes with a similar texture to choose from. Horizon Aquatics notes that dark Seiryu is often picked for the main stone, with lighter Seiryu around it.

When to choose it, and when not to

• Good fit: hard-water fish, tanks where you are buffering hardness deliberately, and anyone happy to keep up frequent water changes.
• Think twice: soft-water species, shrimp tanks, and high-tech tanks running CO2, where stable, soft water matters more than the look of the rock.
• The alternative: dragon stone is inert and gives you a knobbly, cave-like texture instead of sharp peaks.

Whichever you pick, use one rock type throughout the scape. Aquasabi warns that mixing different types of stone costs a layout its harmonious effect. There is more on choosing rock in the aquascaping rocks guide.

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Seiryu stone questions

Does Seiryu stone raise pH?

Yes, slightly. Horizon Aquatics says Seiryu may slightly raise pH, KH, and GH, and Aquarium Science says calcium carbonate stone can’t push pH above about 7.6 to 7.9. Aquasabi and ADA say the effect is stronger if you inject CO2. Frequent, larger water changes with demineralised or reverse-osmosis water keep it manageable.

Is Ryuoh stone the same as Seiryu stone?

Most shops treat them as one. Aquasabi and Horizon Aquatics sell Seiryu and Ryuoh as the same stone, though ADA sells Ryuoh under its own name and Terrarium Tribe reports that some in the trade think they differ. Both harden the water.

Is Seiryu stone safe for shrimp?

It can be, but it isn’t the easy choice. Horizon Aquatics advises checking how the stone has affected your water before adding shrimp, because a higher KH affects Caridina shrimp. An inert stone such as dragon stone or lava rock is the simpler option.

Sources: Aquasabi, Types of hardscape; Aquasabi, Choose your hardscape by weight; Aquasabi, Oliver Knott on water-hardening stones; Horizon Aquatics, Dark Seiryu stone vs Seiryu stone; Terrarium Tribe, Seiryu stone hardscape guide; Aquasabi, Seiryu Ryuoh (shop listing); Aquasabi, Hardscape; Aquasabi, Iwagumi; ADA, Hardscape materials (via Aquasabi); ADA, Layout materials: stones; Horizon Aquatics, Seiryu stone (shop listing); Aquarium Science, Rocks; Buce Plant, Boutique Seiryu Stone (shop listing); Buce Plant, Black Mountain Seiryu Stone (shop listing).

Spider wood is the pale, root-like driftwood that branches out into fine tendrils. It is sold as the root of Rhododendron, or azalea, shrubs, and it suits the Nature Aquarium look because its branching reads as tree roots or bare winter growth at tank scale.

What spider wood is

The trade name covers the roots of Rhododendron, the genus that includes azaleas, which is why you also see it sold as azalea root or redmoor root. Terrarium Tribe and Tannin Aquatics both identify it that way. Tannin Aquatics adds that the exact species and origins are kept “shrouded in a sort of deliberate mystery”, so treat any more precise claim on a product listing with some caution.

It will float at first

Spider wood is lightweight, so it will almost certainly float when it first goes in. That is normal and temporary.

There are three ways round it. Soak it in a separate container until it takes on enough water to sink, which Terrarium Tribe warns can take weeks. Boil it, which helps it sink faster. Or weigh it down in the tank with a piece of dragon stone or another rock and let it waterlog in place.

Why new spider wood floats

It sinks once it has taken on enough water.

How long to boil spider wood

It depends what the boil is for. To clean the wood, Terrarium Tribe recommends 15 to 30 minutes, if you have a pot big enough to hold the piece. To draw tannins out before the wood goes in, Buce Plant recommends boiling for at least one to two hours.

Tannins and tinted water

Like other driftwood, spider wood releases tannins that tint the water amber or brown. Sources disagree on how much. Buce Plant says it releases fewer tannins than other aquarium driftwood, while Tannin Aquatics describes it as releasing a lot. Plan for some tint either way.

Whether the tint is a problem is up to you. Aquasabi suggests filter media such as Seachem Purigen, or simply sitting it out while your regular water changes clear it. Soaking the wood outside the tank for a few days to weeks before use also reduces it. Some keepers want the tint, and a blackwater biotope is built around it.

The white fuzz is harmless

A white biofilm commonly develops in a new spider wood aquarium during the first few weeks, and it looks alarming. Buce Plant calls it harmless and says it disappears on its own. Shrimp and snails graze on it, so there is no need to pull the wood out and scrub it.

Planting on it

The fine branching is ideal for epiphytes, which attach to surfaces instead of rooting in substrate. Tie or glue Java fern, Anubias, or Java moss to the branches and let them take hold. Keep the rhizome above the surface rather than buried.

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Spider wood questions

Does spider wood release tannins?

Yes, though sources disagree on how much. Buce Plant says fewer than other aquarium driftwood, and Tannin Aquatics says a lot. Boiling it for an hour or two, or soaking it for a few days to weeks before use, takes some out first.

How long should you boil spider wood?

Terrarium Tribe recommends 15 to 30 minutes to clean it. If you also want to draw out tannins before it goes in, Buce Plant recommends at least one to two hours.

Should I remove the white fuzz on my spider wood?

No need. Buce Plant describes the white biofilm as harmless and common in the first few weeks, and says it disappears on its own. Shrimp and snails will graze it in the meantime.

Sources: Buce Plant, Spiderwood; Terrarium Tribe, Spider wood guide; Tannin Aquatics, The tangle of Spider Wood; Aquasabi, Driftwood in a tank with invertebrates; Aquasabi, Types of hardscape.

Aquascaping rocks fall into two groups: stones that leave your water alone, such as dragon stone and lava rock, and lime-bearing stones such as Seiryu that slowly harden it. Which group you need depends on your fish, shrimp and plants. Below are the common rocks compared, how much you need, and how to test a stone.

What rock does to your water

This is the bit beginners miss. Carbonate (limestone-type) rocks slowly dissolve and raise your water’s hardness and pH, while inert rocks leave it alone. Aquasabi splits aquascaping stone the same way: rocks like lava and dragon stone do not influence the water, while rugged stones such as Seiryu contain a little lime and may harden it a bit. That is fine for hard-water fish and a problem for soft-water shrimp and plants.

The common aquascaping rocks compared

Aquasabi rates each stone it sells for its effect on water and gives it a bulk-weight factor. The lower the factor, the more stone you get for each kilo.

Stone	Look	Effect on water	Bulk weight
Black lava	Dark and porous	Neutral	0.7
Galapagos rock (lava)	Porous and dark, with brown accents	Neutral	0.9
Tsingy rock	Light grey, often oddly shaped	May harden slightly	0.9
Dragon stone (Ohko)	Brown to reddish, deeply pitted	Neutral	1.0
Seiryu	Grey and rugged, sometimes white-veined	Hardens slightly	1.0
Black pagoda	Dark grey with brown veins, often layered	Hardens slightly	1.0
Black rock	Deep black and broken	May harden slightly	1.0
Elephant skin rock	Lighter grey, roundish and rugged	Hardens slightly	1.1
Yangtse rock	Roundish, in white, yellow, brown or grey	Neutral	1.2
Frodo stone	Grey-brown with deep furrows	Hardens slightly	1.2

A stone that hardens the water slightly does more of it in a tank running CO2. In Aquasabi’s article with aquascaper Oliver Knott, calcareous stones tend to harden the water far more once a CO2 system is running, because the carbonic acid dissolves the lime.

The three you’ll see most

• Seiryu stone: jagged grey rock with white veining. It’s limestone-based, so it raises hardness and pH. The classic Iwagumi stone, but best where hard water suits your livestock.
• Dragon stone (Ohko): tan, knobbly and full of crevices. Water-neutral, and Aquasabi says it crushes into fragments quite easily, so it’s simple to break to size.
• Lava rock: light, porous and dark, with a surface that mosses and ferns root into. Aquasabi calls it neutral, though ADA rates its own KUMU lava as having a moderate effect on hardness.

Torn between the first two? Our dragon stone vs Seiryu page compares them on water, looks and handling.

How much rock you need

Aquasabi’s rule of thumb is your tank’s gross volume in litres divided by six, which gives the weight of stone in kilograms. Then multiply that by the stone’s bulk-weight factor from the table. Its own example: a 54 litre tank works out at 9 kg, which becomes nearly 11 kg of Frodo stone at 1.2, or 7.2 kg of Loa lava rock at 0.8.

Buy more than the sum suggests if the tank will be heavily planted. Aquasabi says at least half of the hardscape will end up hidden behind plants, so start with bigger stones than look right on the first day. It also recommends keeping a spare stash of one kind of stone in several sizes, and making your own small shards with a hammer and chisel, with a cloth over the stone so nothing flies.

How to test a rock

The quick check is an acid test. In Aquasabi’s article with aquascaper Oliver Knott, he drips oak extract onto stones: calcareous rock reacts with clearly visible gas bubbles, and non-calcareous rock does not. Household vinegar is often suggested for the same job, but Aquarium Science warns that drops of vinegar are too weak an acid to fizz on carbonate rock, and recommends a stronger acid such as hydrochloric (pool) acid, which needs careful handling.

The sure check is a soak test. Gensou’s method is to put the clean rock in reverse-osmosis or distilled water, measure GH, KH and pH before it goes in, and test again at 48 hours, one week and two weeks. It also covers what an acid test cannot: Gensou points out that a rock with no carbonate is still not guaranteed to be inert.

Matching rock to your tank

For a soft-water or shrimp tank, lean on a neutral stone such as dragon stone or lava rock, so you aren’t fighting rising hardness. If your fish are happy in harder water, or you’re buffering deliberately, Seiryu is fair game. On looks, jagged Seiryu reads as mountains in an Iwagumi, while chunky dragon stone suits caves, overhangs and texture. Whichever you choose, Aquasabi advises sticking to one kind of stone through a layout.

Stone often shares a layout with wood. Aquasabi recommends black lava, elephant skin rock and Frodo stone alongside driftwood, and our aquarium driftwood guide covers the wood side.

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Questions about aquascaping rock

Do aquascaping rocks change water parameters?

Some do. Carbonate rocks like Seiryu raise hardness and pH as they dissolve. Inert rocks like dragon stone and lava rock do not. An acid test gives a quick answer, and a two-week soak test with GH and KH readings confirms it.

How much rock do I need for my aquarium?

Aquasabi’s rule of thumb is the tank’s gross volume in litres divided by six, in kilograms, then adjusted for the stone: less for light lava, more for dense stone. A 54 litre tank works out at about 9 kg.

Which rock is best for beginners?

Dragon stone. It’s inert, so it will not alter your water chemistry, and its texture is forgiving and easy to arrange into a natural-looking layout.

Can you use rocks collected from outside?

Cautiously. Unknown rocks can change your water in ways an acid test will not show. Gensou warns that rocks containing iron sulphides such as pyrite can release sulphuric acid and lower pH. Soak-test anything you collect, scrub and rinse it thoroughly, and avoid anything metallic, crumbly or from a polluted area.

Sources: Aquasabi, Types of hardscape; Aquasabi, Oliver Knott on water-hardening stones; Aquasabi, Choose your hardscape by weight; Aquarium Science, Rocks; Gensou, How to test if aquarium rocks are safe.