Do Sulawesi Shrimp Eat Algae? What They Graze and What They Ignore

Your rock is growing a fuzz of hair algae, and someone told you a colony of Sulawesi shrimp would clean it up. Sulawesi shrimp do eat algae, but only the thin living film on rock, glass and hardscape, which is mostly diatoms, single-celled algae, bacteria and fine detritus bound together. Hair algae, thread algae and black beard algae stay exactly where they are. So a colony bought as a cleanup crew lets you down twice: the tank still looks green, and the shrimp still need a food supply you have to grow for them. If hair algae is the real problem, Amano shrimp are what people buy for that job, and choosing between Sulawesi shrimp and Amano shrimp really comes down to whether you want a second tank.

Which algae Sulawesi shrimp graze and which they leave behind

They graze what’s microscopic and leave what’s visible, and color has nothing to do with it. What these shrimp work over all day is the patina on hard surfaces: the brown diatom haze on glass, the soft coating on stone, and the bacterial and detritus layer holding it together. Anything with structure you can see and grip is a different kind of food, and it’s the kind they aren’t built to handle.

So how do we know what they actually swallow? The clearest look comes from Caridina spongicola, a small species from the Malili lakes that lives in the cavities of a freshwater sponge. When six specimens were dissected, their guts held a variety of diatoms and none of the sponge’s own spicules. The shrimp were feeding on what builds up on the host, not on the host itself.¹ That fits the wider picture. The Malili shrimp are treated as an adaptive radiation in which most species are habitat specialists, and feeding morphology diversified alongside habitat.² They’re small animals, too. Museum material of the cardinal shrimp, Caridina dennerli from Lake Matano, measured 1.5-3.4 mm carapace length across 53 specimens.³ The evidence describes a fine-particle grazer of that size, and none of it describes anything that strips macroalgae off a tank.

Will Sulawesi shrimp clear the algae already in your tank?

No, and it’s worth being blunt about why, because this mistake is an expensive one. The material they graze is microscopic, the shrimp are tiny, and the water they need sits at the warm, alkaline end of the hobby, around 79-86°F (26-30°C) and pH 7.5-8.5. That’s a system you build around the shrimp, not one you drop them into to fix a maintenance problem. Whatever lives in the tank, visible growth is still answered by the photoperiod, the feeding and the water change routine, and that work stays yours. If you’re shopping for tank-bred Sulawesi shrimp, let it be because you want to keep the shrimp, not because you want a cleaning service.

What has to be growing on the rock before Sulawesi shrimp arrive

A visible film of algae and biofilm, because with these shrimp the food has to exist before the animals do. A freshly filled tank with clean stone gives a grazing specialist almost nothing to eat. An immature system also creates a high risk of early losses, however carefully the shrimp were shipped. The mature, stable setup these shrimp need is their pantry as well.

At Shrimp Aquatics, during the early cycle we normally run the light for 8-10 hours a day so algae and biofilm can establish on the rock and glass. In our systems that natural growth is the main grazing base, and prepared food stays supplemental. The light in a Sulawesi tank is doing a job even when there isn’t a single plant in it. That’s why cutting the photoperiod to fight algae works against you in this particular tank.

Before shrimp go in, look for all three of these together:

• The rock and glass carry a visible film.
• Ammonia and nitrite read zero, so that film is sitting on a working biological filter.
• Temperature and chemistry have held steady for weeks.

How often to feed a Sulawesi colony that already has grazing surfaces

Less than you’d think, and less than the packet suggests. With real grazing surfaces in the tank, the rock feeds the colony continuously, so anything you add is only topping up.

Does that mean these shrimp reject prepared food? No, and the only controlled trial on the group points the other way. In a 2025 rearing study, cardinal shrimp starting at an average total length of 1.445 cm were kept under four combinations of feed and shelter. The groups fed commercial pellets did better on both growth and survival than the groups given only a bacterial starter. Pellets with a Hydrilla shelter produced an average gain of 0.119 cm and 72.727 percent survival over 30 days, while the bacterial starter with a stone shelter produced 0.013 cm and 31.818 percent over 37 days.⁴ Those figures come from one controlled setup, not a forecast for your colony. Still, they’re a fair warning against treating bare rock as a complete diet. They’re also a reason to keep offering a small amount of a suitable food even when the shrimp seem uninterested.

Why leftover food is riskier in a warm alkaline Sulawesi tank

Because warm, alkaline water makes the same amount of ammonia harsher, so taking the leftovers out matters more here than in a cool soft-water shrimp tank. Total ammonia in water sits in two forms, the ammonium ion and un-ionized ammonia, and the un-ionized form is the one that drives ammonia toxicity. Its share rises about ten-fold for each single pH unit, and roughly two-fold for each 10 degrees Celsius of warming.⁵ A Sulawesi tank is warm and alkaline by design. The same total ammonia reading means something harsher in it than it would in a Bee shrimp tank. Warm water also holds less dissolved oxygen than cold water,⁶ and the bacteria breaking down that uneaten pellet are drawing on the same supply.

So read the film on your rock as your feeding schedule. When the stone and glass start to look grazed thin, the fix is more grazing surface, a longer photoperiod or a bigger tank for the number of shrimp you keep. A heavier hand with the food isn’t it. That’s the whole deal with this group: they do eat algae, but you’re the one growing it.

References

6 Sources

1. Caridina spongicola, new species, a freshwater shrimp (Crustacea: Decapoda: Atyidae) from the ancient Malili lake system of Sulawesi, Indonesia, The Raffles Bulletin of Zoology 54(2): 271-276, 2006.
2. Adaptive radiation and ecological diversification of Sulawesi’s ancient lake shrimps (abstract), Evolution 64(11): 3287-3299, 2010.
3. Radiation of endemic species flocks in ancient lakes: systematic revision of the freshwater shrimp Caridina from the ancient lakes of Sulawesi, Indonesia, with the description of eight new species, The Raffles Bulletin of Zoology 57(2): 343-452, 2009.
4. Effect of using different shelter and feed types on growth and survival rate of Sulawesi endemic ornamental shrimps (Caridina dennerli) (journal PDF), Jurnal Ilmiah PLATAX 13(1): 191-204, 2025.
5. Aquatic life ambient water quality criteria for ammonia, freshwater, U.S. Environmental Protection Agency, Office of Water, April 2013.
6. Dissolved oxygen and water, U.S. Geological Survey, Water Science School, updated August 24, 2026.