How to Lower pH in a Sulawesi Shrimp Tank

Is your Sulawesi tank reading above the typical pH range of 7.5-8.5, or still climbing? Don’t reach for an acid: remake the replacement water on a mineral salt that settles lower, then let small water changes carry the tank down over weeks. This is a system built on carbonate hardness. Acid takes the buffer down with the reading. And the minerals that hold that buffer are the ones the shrimp draw on to harden a new shell. So before you touch the water, stop whatever is concentrating minerals in the tank. Everything below is scoped to the lake Caridina kept as Sulawesi shrimp.

Is your Sulawesi tank’s pH actually too high?

Only if it sits above the range the group is kept in, or keeps moving, so check your reading against the table before you do anything. Most freshwater shrimp advice is written for soft, acidic water, and applying it here is how tanks get taken apart.

A single reading at the top of that range isn’t an emergency. What matters more is whether the number is moving. Lake Matano, one of the Malili lakes, has been examined specifically for how its minimal seasonal temperature variability shapes the chemistry of the water column.¹ These are animals from a system that barely changes. If your pH has climbed from 7.8 to above the range over three months, something is accumulating. That’s a different problem from a tank that has sat at 8.4 since the day it was filled.

So what do you do first? Take two readings a week apart before deciding. If the number is stable and inside the range, the honest answer is to leave it alone and put the effort into stability instead. If it has drifted upward, or it’s above the range, work through the sections below in order.

Why pH-down products and active soil break a Sulawesi tank

They lower pH by using up the carbonate hardness that holds the tank steady, so every dose leaves it weaker. Alkalinity is the buffering capacity of the water, the measure of its ability to neutralize acids and hold a fairly stable pH.² It depends on dissolved bicarbonates, carbonates and hydroxides. Water with high alkalinity changes very little in pH when acid enters it, while low alkalinity water can’t keep pace and swings.²

That’s the whole reason a Sulawesi tank holds its numbers, and it’s also why acid doesn’t work as a control here. A dose big enough to actually move the reading has to consume carbonate on its way. What it leaves behind is a tank with less capacity to resist the next change than it had before. It’s a bit like paying off one bill with the money set aside for the next. KH is what keeps pH from swinging, the subject of Sulawesi shrimp KH and alkalinity.

The minerals aren’t decoration either. Research across crustaceans finds that most of the calcium used to harden a new exoskeleton comes from the water, with food, even an eaten shed, adding only a little.³ So a method that pulls minerals out to move a number also takes shell material out of the water your shrimp live in.

What about pressurized carbon dioxide? It’s a separate case. It moves pH without permanently removing carbonate. But it adds a daily rise and fall in the reading, and these animals came from water that doesn’t do that. It also competes with the oxygen problem covered further down. It isn’t a control method for an inhabited Sulawesi tank.

Find what’s pushing your Sulawesi tank’s pH up before you change anything

Find the cause first, because a pH correction that leaves it in place is one you’ll repeat every month. The most common cause is the least dramatic one. Evaporation concentrates dissolved solids in the water that remains.⁴ A Sulawesi tank runs warm enough at 79-86°F (26-30°C) to lose real volume between water changes. Top that loss up with anything carrying minerals, remineralized water and tap water included, and the old minerals stay while new ones pile on top. Over months the whole system concentrates, and the pH goes with it.

Work through these four before you touch the water chemistry.

• Compare your TDS reading now with what it was when the tank was filled. A climb here is the earliest sign of mineral buildup, and it usually shows up well before the pH does.
• Check what you’ve been topping off with. Replace evaporation with pure RO water only, because the minerals that evaporated didn’t go anywhere.
• Look at the hardscape and substrate. Crushed coral, aragonite, shell grit and limestone are all carbonate materials that keep feeding the system. That’s why Sulawesi tanks are set up on inert rock and sand instead.
• Check which mineral salt you’re dosing and what it’s built to buffer at, because that choice sets the pH your replacement water arrives at.

Rebuild your Sulawesi replacement water on a mineral salt that buffers lower

The salt you mix your new water with decides where the tank lands, because once the cause is gone that water is your only real control. Two mineral salts, Sulawesi Mineral 7.5 and 8.5, are widely used for this group, and they aren’t interchangeable.

SaltyShrimp Sulawesi Mineral 7.5 is added to water outside the aquarium, where it dissolves almost totally within seconds with no carbon dioxide or special equipment.⁵ It buffers the pH at around 7.5 and raises carbonate and total hardness at a ratio of KH to degrees dH of 0.42 to 1.0. The manufacturer’s dosage is a slightly heaped measuring spoon, around 3.5 g, to 15 litres of water, for a hardness of around 6 degrees dH and a conductance of around 270 microsiemens.⁵ It names shrimp from lakes Matano, Poso and Towuti, including cardinal shrimp (Caridina dennerli) and harlequin shrimp (Caridina woltereckae).⁵

SaltyShrimp Sulawesi Mineral 8.5 behaves differently. It only dissolves almost totally if carbon dioxide is added for a few days, taking around 3-4 days at a regular quantity of one bubble per second.⁶ The manufacturer tells you to aerate the water afterwards for at least three hours with an air stone to drive that carbon dioxide out before use. It raises carbonate and total hardness at a ratio of KH to degrees dH of 0.78 to 1.0.⁶ The manufacturer states that less finicky Sulawesi shrimp such as the cardinal shrimp can be kept and bred with positive outcomes on both the 7.5 and the 8.5 salt.⁶

Two things follow from that table. At the same general hardness, the 8.5 salt puts noticeably more carbonate hardness into the water than the 7.5 salt does. That’s most of why a tank built on it sits higher. And because the 8.5 salt needs days of carbon dioxide to go into solution, have you been dosing it dry or straight into the display? Then you’ve been adding undissolved carbonate to the tank, and it keeps working long after the water change is over. Prepare mineral salt in a separate container, test it, and only then use it.

Matching your tank to the water the animals were raised in takes one variable out of the move. Most of the systems our tank-bred Sulawesi shrimp come out of are held at those numbers.

Small water changes move a Sulawesi colony down, one correction doesn’t

Once the cause is removed and the replacement water rebuilt, the tank comes down on its own as the old water is replaced. That’s the point. You aren’t adjusting the tank, you’re diluting what it’s currently made of.

1. Confirm ammonia and nitrite both read zero and the tank is otherwise stable. A pH correction on an unstable or incompletely cycled system stacks two problems instead of solving one.
2. Switch top offs to pure RO water and keep them there for good, so the baseline stops climbing while you work.
3. Remove carbonate hardscape and substrate in stages over several weeks. That way the biofilter and the grazing surfaces the colony feeds on aren’t stripped at the same time as the chemistry moves.
4. Mix each batch of replacement water outside the tank on the lower buffering salt, then test its pH, GH and TDS before it goes anywhere near the animals.
5. Exchange a small volume at a time, with the replacement water matched for temperature. Let successive changes carry the tank down gradually.
6. Retest before the next change, and stop if carbonate hardness is approaching the bottom of the 3-6 dKH range.

How fast is too fast? There’s no published safe rate of pH change for these species, so treat any article that gives you one to two decimal places as guessing. The working rule is the cautious one: move less than you think you need to, wait several days, measure, and only then take the next step. If you’re torn between a slower correction and a faster one, take the slower one. Go too slowly and the tank stays high for another two weeks. Go too fast and it shows up as molt trouble in the colony.

Why ammonia is the real danger while your Sulawesi pH sits high

High pH turns more of any ammonia into its toxic form, so the same reading is more dangerous in your tank. Many keepers land on this question because something went wrong, not because a number offended them. If ammonia is part of your picture, here’s what the pH is doing to it. In fresh water, the ratio of unionized ammonia to ammonium ion increases by 10-fold for each rise of a single pH unit, and by approximately two-fold for each 10 degree Celsius rise in temperature between 0 and 30 degrees Celsius.⁷ High outside concentrations of the unionized form let ammonia build up in an animal’s tissues and blood.⁷

That relationship is water chemistry derived by the EPA for freshwater aquatic life in general. It sets no safe or tolerated concentration for any Caridina, and you shouldn’t read one into it. What it does explain is why a warm alkaline tank has a narrower margin for the same total ammonia reading than a cool acidic Bee tank does. It also explains why keepers coming from soft water shrimp find their usual tolerance for a little slack doesn’t carry over.

Keep the aeration running in a warm Sulawesi tank while pH comes down

Keep it at full strength, because cutting gas exchange to shave the pH costs oxygen a warm tank can’t spare. One method that circulates for warm alkaline tanks is to turn down the air and the surface movement so dissolved carbon dioxide builds up and nudges the reading lower. Don’t use it here. Cold water can hold more dissolved oxygen than warm water.⁸ So a tank run at 79-86°F (26-30°C) already has less dissolved oxygen to work with than a room temperature tank at the same level of aeration.

Whatever you gain on the pH reading by throttling gas exchange, you take off an oxygen margin that was thin to begin with, and the bioload hasn’t changed. Keep the aeration and surface movement you have, and aim the outlet so grazing shrimp aren’t pushed around. Let the replacement water do the work on the pH.

What a finished pH correction looks like in a Sulawesi tank

It’s finished when the tank holds its own numbers without you stepping in. Three things should be true across at least two or three weeks of ordinary maintenance. The pH sits inside 7.5-8.5 and stays there between water changes. Carbonate hardness holds inside 3-6 dKH. And TDS comes back to the same place after each change instead of creeping upward.

Read those numbers with the right expectations. pH is reported in logarithmic units, and each whole number represents a 10-fold change in the acidity of the water.⁹ A shift that looks like a rounding error on a test strip isn’t one. That’s why a digital meter that reads to a tenth is worth having here. It’s also why a small drift that won’t go away matters more than its size suggests.

Watch the colony, not just the meter. A settled correction looks like normal grazing across the rock, shrimp out in the open at the usual times and clean sheds in the tank. Shrimp gathering at the surface, hiding for days at a stretch or failing to complete a molt are signs to stop changing anything and recheck the basics.

If pH or carbonate hardness drops below the Sulawesi floor

Stop the water change schedule, and prepare the next batch on a higher buffering mix. Overshooting downward is the risk of doing this well. If pH is heading under 7.5 or carbonate hardness is nearing the bottom of 3-6 dKH, bring that batch in at the same slow pace you used coming down. Don’t dose a carbonate product directly into the display to catch it, and don’t make a second correction while the first one is still moving.

If shrimp are dying while any of this is going on, treat it as a system failure, not a pH number to fix. Check ammonia, nitrite, temperature and TDS first, stop all further chemistry changes, and get the tank stable before you carry on. A colony that has lost animals during a parameter move needs the tank left alone more than it needs the target hit on schedule.

References

9 Sources

1. The biogeochemistry of tropical lakes: A case study from Lake Matano, Indonesia (repository record and abstract), Limnology and Oceanography 53(1), 2008.
2. Alkalinity and Water, U.S. Geological Survey Water Science School, updated August 24, 2026.
3. Biomineralizations: insights and prospects from crustaceans, ZooKeys 176, 2012.
4. Chloride, Salinity, and Dissolved Solids, U.S. Geological Survey Water Resources Mission Area, March 1, 2019.
5. Sulawesi Mineral 7,5, Minerals and trace elements, SaltyShrimp (Garnelenhaus), product technical page.
6. Sulawesi Mineral 8,5, Minerals and trace elements, SaltyShrimp (Garnelenhaus), product technical page.
7. Aquatic Life Ambient Water Quality Criteria for Ammonia, Freshwater, U.S. Environmental Protection Agency Office of Water, April 2013.
8. Dissolved Oxygen and Water, U.S. Geological Survey Water Science School, updated August 24, 2026.
9. pH and Water, U.S. Geological Survey Water Science School, updated August 24, 2026.