Best Rocks for Sulawesi Shrimp

Which rock can you trust in a Sulawesi tank? Porous volcanic lava rock, because it’s inert, so it leaves your water where you set it, and its open pores hold the film the shrimp graze. Ask those two things of any stone: does it change your water, and does it hold a grazing film? Carbonate rock such as limestone fails the first question for good, and any stone you can’t identify gets tested before it goes anywhere near the shrimp.

Which rocks dissolve into Sulawesi water and which ones leave it alone

Carbonate rock dissolves into it, volcanic and dense silicate rock leave it alone, and trade-named aquascaping stone could go either way until you test it. Rock isn’t chemically neutral by default. As water moves through soil and rock, it dissolves small amounts of naturally occurring minerals and carries them along.¹ Calcium and magnesium are the two that show up as hardness. Carbonate rock gives way fastest, because water carrying carbon dioxide becomes carbonic acid, and that acidic water dissolves carbonate rock such as marble, limestone and dolomite.² In a closed aquarium those minerals have nowhere to go. A carbonate rock is a slow, unmetered dose you never chose, a bit like a salt shaker someone left open over the pot.

That splits ordinary aquarium stone into three useful families, plus a fourth group that’s really a marketing label, not a mineral one.

The fourth row is where most Sulawesi accidents start. Two stones sold under the same trade name can come out of different quarries, and a single box can hold one piece that’s quiet in water next to another with calcite running through it. So judge the piece in your hand, not the label on the bag.

Test an unknown rock for carbonate before it goes in the tank

Run two tests, an acid drop and a week in a bucket, on anything that didn’t arrive as plain lava rock. Between them they take about a week, and they answer the question.

1. Dry a clean face of the stone and put a few drops of dilute hydrochloric acid on it. Distinctive effervescence is the definitive sign of carbonate.³ Fizzing anywhere on the piece, including a single seam or vein, is enough to reject it for this tank.
2. Scrub the rock under running water and clear the deep hollows. Packed clay and silt inside a cratered stone will wash out later and settle over the grazing surfaces you’re trying to grow.
3. Put the rinsed rock in a covered bucket of your finished Sulawesi water and record pH, GH, KH and TDS. Leave it a week at room temperature, then read the same four values again.
4. Compare the two readings. A rock that’s holding still reads the same. If the numbers climbed, the stone is dissolving, and it’ll keep doing that in the display tank at a rate you can’t predict.

A week feels long when the scape is half built, we know. It’s still the only way to see what that stone does in your water before your shrimp find out for you.

Why limestone is the wrong way to hold pH 7.5-8.5 in a Sulawesi tank

Because your mineral salt already buffers the water, and limestone adds a second source on top with no dose and no off switch. We understand the pull. The alkaline half of Sulawesi water is what sends keepers toward calcareous rock in the first place, and the mechanism is real. It just solves the problem in the one place you have the least control.

Alkalinity is the water’s capacity to neutralize acids and hold a fairly stable pH, and it comes from dissolved bicarbonates, carbonates and hydroxides.⁴ You already put that in on purpose when you mix your water. A Sulawesi remineralizer added to RO water buffers around pH 7.5 and raises carbonate and total hardness together at a stated ratio.⁵ So the dose you measure into a mixing container is the buffer. A dissolving rock stacks a second source on top of it, one with no dose, no schedule and no off switch, and it works hardest exactly when organic load is pushing pH down and you’d rather know about it.

What about calcium for molting? That argument doesn’t hold up either. Crustaceans take the calcium for a new exoskeleton mainly from the water around them, and food, including a shed shell, is a minor contributor.⁶ The mineral supplements for Sulawesi shrimp you dose are already the calcium supply. Your hardscape doesn’t need to deliver it, and using it that way costs you the ability to hold these four numbers still.

If you’re building a Sulawesi biotope aquarium, accuracy points the same way. Lake Towuti, one of the Malili lakes these shrimp come from, is a tectonic lake seated in ophiolitic rock and surrounded by lateritic soils.⁷ The water is alkaline, but the country around it isn’t limestone. So a calcareous scape isn’t even the faithful choice.

How much grazing texture Sulawesi shrimp need from their rockwork

More than the scape design needs, because the rock is the surface their food grows on. In this group, mature biofilm, aufwuchs and algae are important grazing resources, which makes surface area a husbandry number, not just a matter of looks. A vesicular stone carries a lot of texture per handful, in pores, ridges and shaded hollows. A tumbled cobble the same size carries almost none, so the same footprint of glass leaves the colony far less to graze.

In practice, buy more lava rock than the aquascape design calls for, and pick pieces with visible open pores over dense, glassy ones. Loose rubble in the back corners and under the main structure isn’t wasted. It’s grazing surface. If you want a smoother stone for its looks, make it the visible feature and keep the porous rock as the working volume behind and beneath it.

Can’t you just feed the difference? Not reliably. Acceptance of prepared food varies by species, system and food, so don’t design a low surface scape on the assumption that you can. Supplemental food also can’t make up for a system that hasn’t matured.

Stack Sulawesi rockwork for shelter without trapping waste

Build open stacks with space inside and a gap to the glass, so the shrimp get cover and you can still reach what collects. Shy adults, first week shrimplets and any shrimp still hardening a new shell after a molt all use cover, so the stack needs interior space. The catch is that a sealed pile is also a detritus trap, and this tank is unusually unforgiving about trapped waste. At 79-86°F (26-30°C) and pH 7.5-8.5, more of whatever total ammonia is present sits in the un-ionized form that drives toxicity. The ratio of un-ionized ammonia to ammonium rises about ten-fold for each rise of a single pH unit, and roughly two-fold for each rise of ten degrees Celsius.⁸ So a forgotten pocket of mulm behind a rock matters more here than the same pocket in a cool, acidic Bee tank. It’s also one of the quieter reasons baby Sulawesi shrimp die, since the first-week shrimplets sheltering in that stack are the animals living closest to it.

That’s a design instruction, not a reason to use less rock.

• Leave a working gap between the rockwork and the glass so a siphon can reach behind and under the structure.
• Build open stacks with through paths and gaps at the base. Don’t push a solid wall against the back pane.
• Set the largest pieces directly on the base glass or a thin sand layer so nothing can be undermined and topple onto shrimp.
• Keep any sand or gravel substrate thin, so organic material sits where you can see and remove it.
• Don’t bed the stack into a deep substrate or seal its base, which puts the waste trap exactly where you can’t service it.

Put the rock in before the shrimp so the grazing film is already there

Put the full hardscape in at the start of the cycle, because the rock is the food surface. Assemble the whole structure and run the water at your target chemistry. While the biological filter establishes in the same pores, light and time build algae and biofilm across the exposed faces.

So when is it ready? Stock when the tank tells you: ammonia and nitrite reading zero, temperature and chemistry steady across several days, and a visible, slightly slippery film on the rock. A calendar count of Sulawesi tank cycling time doesn’t prove a tank is cycled. Add shrimp to a clean, bare scape and you’re asking them to graze a surface that has nothing on it yet.

Build a first Sulawesi scape from volcanic rock and test anything you add

For a first Sulawesi tank, we’d build the scape almost entirely from porous volcanic rock and add a single tested feature stone if you want a different shape. That gives you a system where the only things moving your parameters are the ones you added on purpose.

Color also tracks lighting, genetics, nutrition, water chemistry, age and stress, so treat the rock as one input among several. What the stone reliably gives you is a fixed baseline and a large grazing surface, the two things a warm, alkaline, low nutrient tank is hardest to run without. A stack of open volcanic rock with plenty of exposed faces gives tank-bred Sulawesi shrimp the most surface to graze. The scape you build is then the environment they’re moving from rather than a new one they have to adjust to.

References

8 Sources

1. Hardness of Water, U.S. Geological Survey, Water Science School, updated August 24, 2026.
2. Making a Cave, Caves and Karst, U.S. National Park Service, updated May 15, 2023.
3. Limestones, Coal Exploration Core, Kentucky Geological Survey, University of Kentucky.
4. Alkalinity and Water, U.S. Geological Survey, Water Science School, updated August 24, 2026.
5. Sulawesi Mineral 7,5, Minerals and trace elements, SaltyShrimp, product information page.
6. Biomineralizations: insights and prospects from crustaceans, ZooKeys 176, 2012.
7. Geomicrobiological Features of Ferruginous Sediments from Lake Towuti, Indonesia, Frontiers in Microbiology 7, article 1007, 2016.
8. Aquatic Life Ambient Water Quality Criteria for Ammonia, Freshwater, U.S. Environmental Protection Agency, Office of Water, April 2013.