How to Increase KH in a Sulawesi Shrimp Tank

You raise KH in a Sulawesi tank by preparing new water outside the aquarium with a Sulawesi mineral salt that carries carbonate. Then you exchange that water in over several changes until the tank sits inside the range of 3-6 dKH. You don’t raise it by adding carbonate to a stocked tank. 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

Carbonate hardness is the part of your water that absorbs 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. A correction the tank didn’t need isn’t a harmless one in a Sulawesi system, so it’s worth the second test to be sure.

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 and the tank is 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.

This is what makes the distinction between a one-time correction and a routine worth drawing before you mix anything. If the tank drifted down over months and holds steady once you top the KH back up, the ordinary water change cycle simply wasn’t returning as much carbonate as the filter was spending. A properly mineralized change schedule fixes that permanently. If the reading falls again within a week or two of a correction, something is consuming carbonate faster than that. The usual suspects: 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

This is the confusion worth clearing before you buy anything, because the two numbers move for different reasons and the wrong correction leaves the actual problem untouched. 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 they aren’t interchangeable readings.

It matters because of where a shrimp gets its shell. Reviewing biomineralization in crustaceans, Luquet reports that the major source of calcium used for exoskeleton calcification is exogenous, the water in which most crustaceans live.⁴ Food, including consumed exuviae, is a minor contribution to cuticle calcification.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. Conversely, 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

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 a 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

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 relative to the general hardness you’re also setting.

SaltyShrimp’s Sulawesi Mineral 7.5 is the straightforward 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 That ratio is the number to plan around: 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 Caridina dennerli 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.

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. Pouring that into a tank puts solids in the water without putting 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 must not 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 movement.
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

A colony that has been sitting at a low KH has been sitting there for weeks. The reading being wrong isn’t an emergency. A rapid correction would be. Sudden shifts in hardness, pH or TDS are themselves a hazard for shrimp, so the aim is to close the gap a little at a time across your water change schedule.

The practical shape of that? Prepare water whose KH sits above the tank’s current reading, but not at some 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 absorbing 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

The correction is finished when the reading stays put on its own, 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 rather than 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 consumed faster than a normal change cycle returns it needs either the consumption reduced or the change routine adjusted. 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.