Lake Matano Water Parameters and What They Mean for a Shrimp Tank

What is Lake Matano’s water actually like? Its surface is warm, startlingly clear and short of dissolved minerals, at 77-82°F (25-28°C) and pH 8.6 in one study and pH 7.4 in another. Neither set of numbers is what you should aim for at home. Matano is the lake most Sulawesi keepers end up reading about, because the cardinal shrimp lives there and nowhere else. What almost nobody mentions is that the two published sources that put instruments in the lake don’t agree with each other.

What the measurements say about Lake Matano’s surface water

The surface is warm, alkaline, saturated with oxygen and almost empty of nutrients. That’s the picture from the fullest published account, a 2008 study that profiled the lake from the surface down past 500 m.¹ It helps to know what that team was there for: ancient ocean chemistry, not shrimp. The water they describe is a by-product of that work, which is why the figures arrive in a chemist’s units instead of a hobbyist’s.

Which rows should catch your eye? Two of them. The surface sits at a pH of 8.6, higher than almost any tank you’ll see these shrimp in. And the phosphate reading is so low you’d never get a hobby kit to show it. Hold on to both, because they come back later.

Why the deep half of a Lake Matano profile has nothing to do with your tank

The deep half of Lake Matano has lost its oxygen, so it isn’t shrimp habitat at all. The lake doesn’t turn over. A lasting density boundary sits near 100 m, and everything under it has been cut off from the air long enough to lose its oxygen.¹ Below that boundary the same study measured dissolved oxygen under 1 µmol/L and dissolved iron around 140 µmol/L.¹ That’s not a habitat with slightly different chemistry. It’s water nothing with gills can use.

Why does that matter to you? Because most of the Lake Matano data you’ll find online is deep-water data, the part scientists find interesting. If a table quotes you an iron concentration, a methane figure or a pH of 7.00 for Lake Matano, it’s describing water hundreds of meters below anything a shrimp has seen. Read the depth column before you read the number.

What Lake Matano’s clarity tells you about feeding a Sulawesi tank

The lake is clear because almost nothing grows in it, which tells you to grow food on surfaces and go easy on prepared food. Sunlight still reaches under 130 m, and the measured rate of photosynthesis in the surface water sits in the same territory as ultra-oligotrophic lakes in the high arctic.¹ The reason is that phosphate row. Iron particles sinking through the water strip phosphorus out of the sunlit layer, so the algae never get going.¹

So what’s a Lake Matano shrimp eating? A thin, slow-growing film on rock, in water with next to no nutrients in it. That’s a very different animal from one evolved to find a meal, more a patient grazer on a lean diet than a scavenger waiting for dinner. If one thing here changes what you do tomorrow, make it this: grow the surfaces before you buy the shrimp, and treat prepared food as an occasional extra. Lifting anything uneaten within a few minutes is the usual rule. It matters more here than in a cool tank, because warm water works through leftovers fast.

Why a second published source gives Lake Matano a different pH

Because the 2009 taxonomic revision of the Sulawesi Caridina species reports its own figure, a lower one, in a one-line habitat note the hobby has mostly skipped. It puts Lake Matano at a pH of 7.4 with a conductivity of 224 µS, and gives temperatures across Matano, Mahalona and Towuti of 81-88°F (27-31°C).² It also says a stable thermocline or chemocline is basically missing in these lakes.²

Now set that beside the table above. One source has a permanently stratified lake with an alkaline surface at a pH of 8.6. The other has a well-mixed lake at a pH of 7.4. Those can’t both be a full description of the same water.

Which would we trust? For the water itself, the 2008 profile. Measuring the lake was the whole point of that study, and it reports a full depth series, not a single line. The 2009 figures read like spot readings taken on a collecting trip. That’s a reasonable thing for a taxonomist to jot down and a poor thing to build a tank on. Still, we’d rather tell you the two disagree than pick one and pretend the question is settled. Nobody has published a modern survey of the shallow margins where these shrimp actually live.

Whether to copy Lake Matano’s numbers into your own tank

No, and you couldn’t if you tried. A lake that deep holds its chemistry steady through sheer volume. A 20 gallon glass box has no such buffer, so the only way to get stability at home is to build the water deliberately and hold it there. That’s what the numbers below are for.

Temperature is the one place the lake and the tank nearly agree

Both published figures for the lake sit inside or just above the band these shrimp are kept in. That’s the main reason the band looks the way it does. Want the reasoning behind it, and what running warm costs you in oxygen? That belongs with why Sulawesi shrimp need warm water. What the lake adds is a warning about chasing the top of the band. The higher of the two published readings is a single spot measurement in a body of water that can absorb it. Your heater in a small tank can’t.

The lake is far softer than the water these shrimp are kept in

This is the real surprise. A conductivity of 224 µS is dilute, mineral-poor water, and the sulfate and phosphate readings say the same thing from a different direction. Yet we keep these shrimp at 150-250 ppm TDS. Why the gap? Because the mineral load in a tank isn’t only feeding the animal. It holds your KH up so the pH doesn’t slide. It also replaces the dissolved calcium and magnesium that a lake renews all the time and a closed tank doesn’t. Mixing replacement water to the numbers above, outside the tank, is covered properly in the guide to Sulawesi shrimp care parameters.

Which Sulawesi shrimp the Lake Matano numbers actually apply to

They apply to the shrimp that come from Lake Matano itself, not to every line sold as Sulawesi shrimp. Matano is one lake in the Malili system, and its shrimp are its own. Caridina dennerli, the cardinal or Sulawesi White Sock shrimp, is endemic to Lake Matano and found nowhere else.³ Plenty of the lines sold as Sulawesi shrimp don’t come from Matano at all, and a Matano reading isn’t their habitat. Which line belongs to which lake is the job of the guide on where Sulawesi shrimp come from. It’s worth sorting out before you treat any lake figure as a target.

There’s a harder fact attached to the cardinal shrimp. It was assessed in 2018 as Critically Endangered and tagged Possibly Extinct in the Wild, after surveys in 2017 and 2018 recorded no specimens. The assessment lists dams and water management, industrial effluents and agricultural runoff among the threats.³ Whatever the lake measured in 2008, it isn’t measuring that now, and nobody is going to settle the disagreement above with fresh field data soon.

That is also the practical reason to buy tank-bred. Every line in our Sulawesi shrimp range is bred here, not collected. A tank-bred shrimp reaches you from water somebody can give you the readings for, which a wild-caught one never does.

References

3 Sources

1. Photoferrotrophs thrive in an Archean Ocean analogue, Crowe et al., Proceedings of the National Academy of Sciences 105(41), 2008.
2. Radiation of endemic species flocks in ancient lakes: systematic revision of the freshwater shrimp Caridina from the ancient lakes of Sulawesi, Indonesia, von Rintelen and Cai, Raffles Bulletin of Zoology 57(2), 2009.
3. Caridina dennerli, IUCN Red List assessment, von Rintelen, K., IUCN Red List of Threatened Species, assessed 2018.