How to Increase KH in a Sulawesi Shrimp Tank

Has your Sulawesi tank’s KH test come up short of 3 dKH? Raise it by preparing new water outside the aquarium with a Sulawesi mineral salt that carries carbonate, then exchanging that water in over several changes until the tank sits inside 3-6 dKH. Don’t raise it by adding carbonate to a stocked tank. And crushed coral in the filter is a safety net against acid drift, not a way to lift a low reading.

Confirm your Sulawesi tank is really below 3 dKH before you change anything

Confirm it with a second test first, because a low KH reading means the buffer that holds your pH steady is running out, and a correction the tank didn’t need does harm of its own. Carbonate hardness is the part of your water that soaks up acid instead of letting it move the pH. The U.S. Geological Survey defines alkalinity as the buffering capacity of a water body, a measure of its ability to neutralize acids and so maintain a fairly stable pH.¹ It describes alkalinity as a property produced chiefly by dissolved bicarbonates, carbonates and hydroxides, not a substance of its own.¹ That’s the job KH is doing in a Sulawesi tank. Why does a low reading matter more here than the number suggests? Because once the buffer is spent, nothing is holding the pH. How GH and pH ride on that same buffer is set out in Sulawesi shrimp KH and alkalinity.

Run the test again before you accept it. A single reading is easy to misread, and easier still when you’re already expecting a low result. Test a second sample drawn from a different part of the tank. If you have a second kit or an unopened bottle of reagent, use that too and compare. In a Sulawesi system, a correction the tank didn’t need isn’t harmless, so the second test is cheap insurance.

Then read the result against the whole profile, not against KH alone. If pH is still sitting inside 7.5-8.5 and TDS is inside 150-250 ppm, a KH reading a little under the range is a slow drift, and you have time to correct it properly. If pH has fallen out of range with it, the buffer is already spent. The tank is then changing faster than a weekly routine will catch.

What keeps pulling KH down in a closed Sulawesi tank

The biggest consumer is the filter you built on purpose. The EPA’s guidance on nitrification records that a reduction of total alkalinity may accompany nitrification, because a significant amount of bicarbonate is consumed in the conversion of ammonia to nitrite.² It lists falling pH and alkalinity as a symptom of nitrification, and cites a model indicating that 8.64 mg/L of bicarbonate will be utilized for each mg/L of ammonia-nitrogen oxidized.² In a closed aquarium, nothing puts that bicarbonate back except you.

So is this a one-time correction or a routine problem? It’s worth knowing before you mix anything. If the tank drifted down over months and holds steady once you top the KH back up, your ordinary water changes simply weren’t returning as much carbonate as the filter was spending. A properly mineralized change schedule fixes that for good. If the reading falls again within a week or two of a correction, something is eating carbonate faster than that. The usual suspects are a heavier bioload than the tank had before, uneaten food breaking down, or a substrate that’s actively working against you. An active soil made for soft-water Bee shrimp will strip carbonate out of Sulawesi water until its exchange capacity runs out, and no amount of remineralizing wins that argument. Sulawesi tanks want inert substrate and hardscape.

Raising KH won’t fix a soft molt or a low GH reading

No, because GH and KH are different readings that move for different reasons, and the wrong correction leaves the actual problem untouched. Clear this up before you buy anything. Water hardness in the GH sense is, in the USGS definition, the amount of dissolved calcium and magnesium in the water.³ KH is the carbonate and bicarbonate side. They’re related in practice because most aquarium mineral products carry both, but you can’t swap one reading for the other.

It matters because of where a shrimp gets its shell. A review of biomineralization across crustaceans finds that most of the calcium for a new exoskeleton comes from the water, with food, even an eaten shed, adding only a little.⁴ So if you’re seeing failed or incomplete molts in Sulawesi shrimp and reaching for a KH product, you’re adjusting the wrong half of the water. Check GH against 4-8 dGH first. The reverse holds too: if pH is wandering between tests while GH looks fine, KH is the number to work on.

Which method actually moves KH in water that’s already alkaline

Prepared remineralized water, because it’s the only common method that lets you set the number before it reaches the shrimp. Three approaches get recommended for shrimp tanks generally, and they behave very differently in a system that’s already sitting near pH 8.

Prepared water is the method the rest of this guide follows, because it’s the only one of the three where you decide the number instead of discovering it. Carbonate media still earns a place in the filter. It reacts to acid, which is exactly what nitrification keeps producing, so it works as a floor under the tank between your water changes. Treat it as insurance, not as the correction.

Mix the Sulawesi salt outside the tank, because Mineral 8.5 won’t dissolve without CO2

Mix it in a separate vessel, because Mineral 8.5 needs days of CO2 to dissolve and even the easier salt should be tested before it reaches your shrimp. Start from RO or RO/DI water, so you know the mineral content is only what you put in. Then choose the salt by how much carbonate you need compared with the general hardness you’re also setting.

SaltyShrimp’s Sulawesi Mineral 7.5 is the easy one. The manufacturer states that it’s added to water outside the aquarium, will almost totally dissolve within seconds, and that the water is ready for use immediately.⁵ It buffers the pH at around 7.5 and raises carbonate and total hardness at a ratio of KH/dH = 0.42/1.0.⁵ The stated dose is a slightly heaped measuring spoon of around 3.5 g to 15 litres of water, for around 6 dH and a conductance of around 270 +/- 40 microsiemens. The page names shrimp from lakes Matano, Poso and Towuti, including cardinal shrimp (Caridina dennerli).⁵ Plan around that ratio. It tells you the salt sets your GH and your KH together, so you can’t use it to move KH alone.

Sulawesi Mineral 8.5 carries proportionally more carbonate, at a stated ratio of KH/dH = 0.78/1.0.⁶ The manufacturer notes that less finicky Sulawesi shrimp such as the cardinal shrimp have been kept and bred with positive outcomes on both salts.⁶ It’s the one to reach for when your target KH sits at the upper end of the range while GH stays moderate. It’s also the one that won’t simply stir in, as anyone who has stared at a cloudy bucket can tell you.

Dissolving Mineral 8.5 takes CO2 and at least three hours of aeration afterward

1. Add the salt to RO water in a vessel outside the aquarium. The manufacturer states it will almost totally dissolve if CO2 is added for a few days.⁶ On a regular CO2 quantity of one bubble per second, the salt dissolved totally in approximately 3-4 days.⁶
2. Leave the CO2 running until the cloudiness is gone. A suspension that still looks milky has undissolved mineral in it. Pour that into a tank and you put solids in the water without getting the carbonate into solution, where the test kit and the shrimp would meet it.
3. Remove the CO2 and aerate. The manufacturer instruction is explicit: if you use CO2 to dissolve the mineral salt, aerate the water afterward for at least three hours with an air stone in order to expel the CO2.⁶ Water still carrying dissolved CO2 reads far more acidic than the salt is meant to produce, and that’s the state you mustn’t introduce to a stocked tank.
4. Bring the vessel to the tank’s temperature, inside 79-86°F (26-30°C), and hold it there while it aerates. That way you aren’t correcting hardness and temperature in the same move.
5. Test the finished water for pH, KH, GH and TDS before you use any of it. This is the step that makes the whole method safe, and skipping it turns a controlled correction back into a guess.

Bring the prepared water in across several changes rather than one

Bring it in a little at a time across your normal water changes, because the low reading isn’t the emergency and a rapid correction would be. A colony that has been sitting at a low KH has been sitting there for weeks. Sudden shifts in hardness, pH or TDS are a hazard for shrimp in their own right, so the aim is to close the gap gradually.

What does that look like in practice? Prepare water whose KH sits above the tank’s current reading, but without a dramatic overshoot. Exchange a modest volume, then let it settle before you measure again. Deliver it slowly, by drip line or by pouring against the glass over a long stretch. Match the temperature first, so the shrimp aren’t taking a thermal change and a chemical one at once. Then stop and wait. Don’t repeat the change the same day.

Shrimp Aquatics doesn’t publish an exact permissible change per hour or per session for this. No measured tolerance for a rate of KH or TDS change has been established for these species. What you can do is make the size of each step visible to yourself. Record the tank’s KH, GH, TDS and pH before the change and again once the tank has mixed. Then you know how far a given volume actually moved the reading, and you can use that to size the next one. A step you can measure is a step you can make smaller.

How to tell whether the KH you added is actually holding

It’s holding when the reading stays put on its own through a full change cycle, not when it first touches the range. Give the tank a full cycle between water changes and check the following.

• KH is inside 3-6 dKH on a fresh test, and reads the same at the end of the interval as it did at the start.
• pH has settled inside 7.5-8.5 and is no longer moving noticeably between tests.
• GH and TDS landed where you intended, at 4-8 dGH and 150-250 ppm, and didn’t climb along with the KH.
• Ammonia and nitrite are still reading zero, since a bioload change is one of the things that empties KH quickly.
• KH is back down before the next scheduled change. That’s an ongoing drain, not an under-dose, and repeating a larger correction won’t fix it.

If it does slide again, go back to the causes, not the cure. Look at what the tank is being fed, whether the substrate is inert, and whether the stocking or feeding changed around the time the drift started. A tank whose carbonate is being used up faster than a normal change cycle returns it needs either less consumption or a different change routine. A stronger dose substitutes for neither. Once the reading holds through a full change cycle, the tank is finally ready to carry more animals. The advanced and expert care levels marked on our Sulawesi shrimp listings are worth reading against the KH your tank actually holds, not the one you were aiming for.

References

6 Sources

1. Alkalinity and Water, U.S. Geological Survey, Water Science School, updated August 24, 2026.
2. Nitrification, U.S. Environmental Protection Agency, Office of Water, Office of Ground Water and Drinking Water, August 15, 2002.
3. Hardness of Water, U.S. Geological Survey, Water Science School, updated August 24, 2026.
4. Biomineralizations: insights and prospects from crustaceans, Gilles Luquet, ZooKeys 176, 103-121, 2012.
5. Sulawesi Mineral 7,5, Minerals and trace elements, SaltyShrimp (Garnelenhaus), manufacturer product information page.
6. Sulawesi Mineral 8,5, Minerals and trace elements, SaltyShrimp (Garnelenhaus), manufacturer product information page.