Why do Sulawesi shrimp need alkaline water when so many other shrimp in the same genus are kept soft and acidic? Because it’s the water they evolved in, and nothing in a closed aquarium replaces it. The lake-system Caridina sold under this name come from two ancient lake systems on one Indonesian island, Lake Poso and the Malili lakes, and from nowhere else.¹ In your tank, the useful part of that answer isn’t the pH number itself. It’s what holds the number up: a carbonate reserve that keeps pH from sliding down between water changes, in water that stays surprisingly low in dissolved minerals.

How alkaline is the water Sulawesi shrimp actually come from?

Less alkaline than the hobby usually assumes, and much more dilute. Lake Towuti, one of the Malili lakes, has surface water described as circumneutral at about pH 7.8, a conductivity of only 210 microsiemens per centimeter, and a chemistry dominated by magnesium and bicarbonate.² So it’s a lake with a mineral profile most keepers would call soft, sitting at a pH most keepers associate with hard water.

pH 7.8Lake Towuti surface water, measured

210microsiemens per centimeter, a dilute lake

Mgmagnesium and bicarbonate dominated

That combination is the whole difficulty of the group, and it’s why two opposite mistakes both fail. Build the tank on an active soil and you get the low mineral content but lose the pH. Build it on hard tap water, crushed coral or limestone hardscape and you get the pH but overshoot the minerals badly. Neither one gives you a lake that’s alkaline and dilute at the same time. That’s why Sulawesi water is prepared, not found.

What alkaline, mineral-bearing water does for a Sulawesi shrimp at every molt

It supplies the shell. Growth in a shrimp happens only at a molt, and all freshwater prawns, like other crustaceans, have to regularly cast the exoskeleton in order to grow.³ Every increase in size is a discarded shell and a new one that has to harden. That rebuild is where the water stops being background and becomes a supply line.

Where does the calcium for that new shell come from? Mostly from the water the animal lives in, which is what crustacean research finds across the group.⁴ That’s the reason GH is treated as a live number on this tank, something you keep testing, instead of something set once at fill.

The second job the water does is more immediate: it keeps the tank from moving. That’s the part you control week to week, and it’s measured with the wrong test kit almost every time.

KH, not pH, is the number that holds a Sulawesi tank steady

KH measures the carbonate reserve that stops pH from moving, so it tells you more about a Sulawesi tank’s stability than a pH reading can. Alkalinity is the buffering capacity of a water body, a measure of its ability to neutralize acids and so maintain a fairly stable pH. It isn’t a chemical in the water but a property of the water, dependent on what’s dissolved in it, chiefly bicarbonates and carbonates.⁵ Water with high alkalinity experiences less of a change in its own acidity when acid is introduced into it.⁵ Your KH test kit is the aquarium measure of that reserve, and pH quietly depends on it, the subject of Sulawesi shrimp KH and alkalinity.

Think of pH as where the water is standing right now, and KH as whether it’ll still be standing there next week. A Sulawesi tank reading pH 8.0 with almost no carbonate hardness left isn’t a stable tank. It’s a tank that hasn’t drifted yet. That’s also why pH-up products and buffer additives disappoint when you use them to raise pH for Sulawesi shrimp. They move the reading without building the reserve, and the reading comes back down.

Typical water targets for lake-system Sulawesi *Caridina*
pH	7.5-8.5
Carbonate hardness (KH)	3-6 dKH
General hardness (GH)	4-8 dGH
TDS	150-250 ppm
Temperature	79-86°F (26-30°C)
Nitrate	Aim for under 10 ppm; that’s a target, not a tolerance limit

These are typical ranges for the group, not survival limits, and an individual species or line can carry a narrower verified range. Where a listing states its own numbers, those are the ones to match.

Why other Caridina care sheets tell you to use soft, acidic water

Other Caridina care sheets call for soft, acidic water because they’re written for Bee and Crystal shrimp, which share the genus name with Sulawesi shrimp but not their water. Caridina is a large genus, and the lines that made it famous in the hobby are the soft-water ones. Bee and Crystal shrimp are kept at pH 5.8-6.8, KH 0-2 dKH, GH 4-6 dGH, TDS 100-150 ppm and 60-72°F (15.5-22°C), normally over an active substrate chosen precisely because it pulls pH down and holds it there.

That’s the opposite water in every column. Same genus, opposite tank, which is a bit like two cousins who can’t agree on the thermostat. The substrate is where that confusion turns into a real problem.

Don’t build a Sulawesi tank on an active substrate

An active shrimp soil is engineered to lower pH and consume carbonate hardness. In a Sulawesi tank it works directly against the reserve you’re trying to hold, and adding minerals on top of it doesn’t remove that pull. Inert substrate and inert hardscape are the default for this group.

At Shrimp Aquatics we commonly use Sula Sand Volcanic Rock in our Sulawesi systems because it’s inert and has worked well in tanks where we need pH to remain steady.

The distinction matters when you buy as much as when you set up. If your shrimp came from a Sulawesi shrimp listing, a Crystal Red care sheet is describing the opposite water, not a stricter version of yours.

Warm alkaline water makes ammonia more dangerous in a Sulawesi tank

The cost of alkaline water in a Sulawesi tank is ammonia: the same ammonia reading is more toxic at high pH and temperature. In fresh water, total ammonia sits in two forms, the ammonium ion and un-ionized ammonia, and it’s the un-ionized form that drives toxicity. The ratio of un-ionized ammonia to ammonium ion in fresh water increases by 10-fold for each rise of a single pH unit. It rises by approximately two-fold for each 10 degree Celsius rise in temperature between 0 and 30 degrees Celsius.⁶ High external un-ionized ammonia concentrations reduce or reverse diffusive gradients and cause the buildup of ammonia in internal tissues and blood.⁶ Those are general freshwater criteria, so take the direction from them, not a safe number.

Read your ammonia result against your pH

A total ammonia figure that would be a minor problem in a cool, slightly acidic tank isn’t the same figure at pH 8.2 and 86°F. On this group, ammonia and nitrite belong at zero before any shrimp goes in, and the system has to be mature enough to keep them there.

That’s the practical trade. The same warm, alkaline water that suits these shrimp is also less forgiving of uneaten food, a heavy stocking level or a filter that hasn’t fully established. That’s why the group is kept in mature systems with grazing surfaces already grown in, and fed sparingly. A cycled tank here means ammonia 0 and nitrite 0 with an established biological filter and visible biofilm, not a number of weeks marked off on a calendar.

How to hold pH and KH steady in a Sulawesi tank

Keeping pH and KH steady in a Sulawesi tank after you’ve prepared the water comes down to three habits.

Prepare new water with a mineral built for this water. A Sulawesi remineralizer has to add carbonate hardness alongside general hardness, and that isn’t what a soft-water product is designed to do. SaltyShrimp states that its Sulawesi Mineral 8.5 raises carbonate and total hardness at a ratio of KH per degree of total hardness of 0.78 to 1.0.⁷ A mineral sold for Bee and Crystal tanks is made for water with almost no carbonate hardness at all. It won’t build the reserve this group runs on. Follow the current manufacturer instructions for whichever product you use. Then test the finished pH, GH, KH and TDS before that water goes anywhere near shrimp.

Top off evaporation with RO water alone. As a physical matter, evaporation concentrates the dissolved solids left behind in the water that remains.⁸ Water leaves the tank and minerals don’t. So if you top off with prepared mineral water, TDS climbs week after week while the water level looks perfectly correct.

Change water in small, matched volumes. Match the replacement water to the tank on temperature, pH, KH, GH and TDS before it goes in. An unmatched change is itself the swing you were trying to avoid. Small and frequent beats large and occasional on a tank whose whole requirement is stability.

Test KH on a schedule, not only when something looks wrong. It’s the number that moves first.
Track TDS between water changes. A steady climb usually points at top-off water, not a chemistry problem.
Keep substrate, rock and hardscape inert, so nothing in the tank is quietly working against the buffer.
Recheck the finished parameters of prepared water every time, not only when you open a new bag of mineral.
Don’t chase a pH reading with buffers or pH-up products while KH is falling. Rebuild the reserve and the reading follows.

If you track one number on this tank, make it KH. pH is the symptom you’ll notice and the one every care sheet argues about, but carbonate hardness is what actually moves. Hold your KH between water changes and your pH stops being interesting.

What the research says about alkaline water for Sulawesi shrimp

Start with the gap, because it shapes how you read everything else. No published study has measured how a Sulawesi Caridina responds to a change in pH. So nobody can tell you exactly what acidic water does to your shrimp and call it a measured finding. What’s documented is where these shrimp live, what that water measures, and how water chemistry behaves for crustaceans in general. That’s enough to explain the requirement and to run the tank well.

The calcium point comes from crustaceans as a whole. Across crustaceans, the major source of the calcium used for exoskeleton calcification is exogenous, meaning the water the animal lives in. Stored premolt reserves and food, including a consumed molt, contribute less.⁴ The point that growth happens only at a molt comes from the FAO manual on farming freshwater prawns.³ Both are crustacean-level results, not measurements on Sulawesi Caridina, so read them as the mechanism behind the advice to keep GH steady.

The ammonia figures come from the EPA’s freshwater criteria. Those criteria were derived for the freshwater assemblage the EPA assessed, not for shrimp, and they set no aquarium threshold.⁶ The direction of the relationship is what you use: higher pH and warmer water put more of the same total ammonia into its toxic form.