What a Siamese Algae Eater Is and What It Does

A Siamese algae eater is a freshwater fish native to Southeast Asia that eats algae off tank surfaces and plants. Unlike many fish sold as "algae eaters," the true Siamese algae eater (Crossocheilus siamensis) actually consumes algae throughout its life, not just when young. It will graze on green algae, black beard algae, and thread algae that coat rocks, driftwood, and plant leaves.

The fish reaches 5 to 6 inches long and has a tan or olive body with a dark stripe running from head to tail. It is active during the day, constantly moving along surfaces and through plants. A single Siamese algae eater can noticeably reduce algae in a 20-gallon tank or larger, though it works best as part of a broader tank maintenance routine—regular water changes and moderate lighting still matter.

Siamese algae eaters are not aggressive toward most fish, but they can become territorial with each other as they mature. Keeping more than one in the same tank often leads to chasing and stress, so most aquarists keep just one per tank unless the tank is very large (55 gallons or more) and heavily planted.

Key Takeaways

  • Siamese algae eaters eat algae consistently throughout their lives, making them more reliable than plecos or Chinese algae eaters for long-term algae control.
  • They need a tank of at least 20 gallons with plenty of surfaces—rocks, driftwood, and plants—where algae naturally grows for them to graze.
  • Keep only one per tank in most setups, as they become territorial with each other and will chase and stress tank mates of the same species.
  • They live 5 to 8 years in captivity and require stable water conditions: temperature between 72 and 82 degrees Fahrenheit, neutral to slightly acidic pH, and moderate current.

Tank Size and Water Conditions

A Siamese algae eater needs a minimum of 20 gallons, though 30 gallons or more gives it room to establish a territory and move freely without constant conflict with tank mates. The fish is active and does not thrive in cramped spaces. If you plan to keep one with other bottom-dwelling fish, add 10 gallons per additional species to reduce territorial disputes.

Water temperature should stay between 72 and 82 degrees Fahrenheit. The fish tolerates a range but performs best in the middle of that band—around 75 to 78 degrees. pH should be neutral to slightly acidic (6.5 to 7.5). Siamese algae eaters are sensitive to ammonia and nitrite, so the tank must be fully cycled before you add one, and weekly water changes of 25 to 30 percent are necessary to keep nitrate levels low.

Moderate water flow is beneficial. The fish comes from streams in its native habitat and appreciates gentle current from a filter outlet or powerhead. Stagnant water can stress it and make it more prone to disease. A standard aquarium filter rated for your tank size is sufficient; you do not need specialized equipment.

Feeding and Diet Beyond Algae

Siamese algae eaters eat algae, but algae alone is not enough nutrition. In a new tank or one with very little algae growth, the fish will go hungry if you do not supplement. Offer blanched vegetables two to three times per week: zucchini, cucumber, or spinach placed on a small dish or weighted down with a rock so it sinks. Leave the vegetable in the tank for a few hours, then remove any uneaten portion.

You can also provide sinking pellets formulated for algae eaters or bottom feeders. Feed a small pinch once or twice daily, only as much as the fish will eat in a few minutes. Overfeeding fouls the water and reduces the fish's motivation to eat algae. In a mature, well-lit tank with moderate algae growth, a Siamese algae eater may need little supplemental food beyond what it grazes naturally.

Avoid feeding dried bloodworms or other high-protein foods regularly. These can cause digestive problems and shift the fish's diet away from algae. The goal is to keep it grazing, not to turn it into a carnivore.

Tank Mates and Temperament

Siamese algae eaters are peaceful with most community fish: tetras, rasboras, corydoras catfish, and peaceful gouramis coexist without problems. They do not nip fins or chase smaller fish. However, they can be aggressive toward other algae eaters and bottom-dwelling fish that compete for the same space and food. Avoid keeping them with Chinese algae eaters, plecos, or other Siamese algae eaters unless your tank is very large and heavily planted.

They may chase or stress aggressive fish like cichlids or large plecos that also occupy the bottom of the tank. In a heavily planted tank with plenty of hiding spots, conflicts are less likely because each fish can claim its own territory. In a sparse tank, territorial disputes escalate quickly.

Siamese algae eaters are not safe with very small shrimp or fry, as they may eat them. They are generally safe with adult shrimp and snails, though some individuals will nibble on snail antennae or harass slow-moving species. Observe your fish for the first week to confirm compatibility.

Lighting and Plant Considerations

Algae growth depends on light, so the amount of light in your tank directly affects how much food your Siamese algae eater has access to. A tank with 8 to 10 hours of light per day and moderate intensity (not high-intensity planted tank lighting) will grow enough algae to keep the fish grazing without becoming overgrown. Tanks with very low light may not produce enough algae, leaving the fish dependent on supplemental food.

Live plants benefit the setup in two ways: they compete with algae for nutrients, reducing excessive algae blooms, and they provide surfaces where algae naturally accumulates for the fish to eat. Slow-growing plants like anubias and java fern are ideal because they do not require high light and will not be uprooted by the fish's constant movement along the substrate.

Avoid very bright lighting (10+ hours daily with high-intensity fixtures) unless you are running a planted tank with regular fertilization and CO2. Excessive light without plant management leads to algae blooms that become unsightly and can suffocate plants and fish.

Common Health Issues and Prevention

Siamese algae eaters are hardy when water conditions are stable, but they are prone to stress-related illness if kept in poor conditions or with aggressive tank mates. Signs of stress include hiding constantly, refusing to eat, and developing a pale or darkened coloration. Ich (white spot disease) can appear after temperature fluctuations or exposure to new fish carrying the parasite.

Prevent illness by maintaining consistent water parameters, performing regular water changes, and avoiding overcrowding. Quarantine new fish for two weeks before adding them to the main tank to reduce the risk of introducing disease. If your Siamese algae eater shows signs of illness, raise the temperature gradually to 80 degrees Fahrenheit and perform daily 25 percent water changes. Most stress-related issues resolve within a week if water quality improves.

Avoid medications containing copper, as Siamese algae eaters are sensitive to it. If treatment is necessary, use copper-free remedies or consult a resource focused on freshwater fish disease management.

Distinguishing True Siamese Algae Eaters from Lookalikes

The aquarium trade often sells fish labeled as "algae eaters" that are not true Siamese algae eaters. The most common impostor is the Chinese algae eater (Gyrinocheilus aymonieri), which looks similar but becomes aggressive and territorial as it matures. Chinese algae eaters also stop eating algae after a few months and instead harass other fish and plants.

True Siamese algae eaters have a dark stripe that runs the full length of the body from the mouth to the tail fin. The stripe is thin and distinct. Chinese algae eaters have a thicker, more irregular stripe and a larger, more rounded head. When shopping, ask the store for Crossocheilus siamensis by scientific name if you are unsure. Reputable aquarium stores can confirm the species.

Another lookalike is the flying fox (Epalzeorhynchos kalopterum), which is more aggressive and does not eat algae reliably. Flying foxes have a red or orange stripe along the body, whereas Siamese algae eaters have a black stripe on a tan background.

Frequently Asked Questions

Will a Siamese algae eater eat all the algae in my tank?

A single Siamese algae eater will significantly reduce algae but rarely eliminate it entirely. The fish eats green algae and thread algae consistently but may not touch all types of black beard algae or stubborn brown algae. Regular water changes and moderate lighting remain necessary for overall tank balance.

Can I keep two Siamese algae eaters together?

Not in most tanks. They become territorial as they mature and will chase and stress each other. Only consider keeping two if your tank is 55 gallons or larger, heavily planted with many hiding spots, and you introduce them at the same time as juveniles. Even then, conflicts may develop.

How long do Siamese algae eaters live?

In a well-maintained tank, a Siamese algae eater typically lives 5 to 8 years. Some individuals reach 10 years with excellent care. Lifespan depends on water quality, diet, and tank mates. Stress from poor conditions or aggressive tank mates shortens life expectancy.

What should I do if my Siamese algae eater stops eating algae?

If the fish stops grazing, check water parameters first—ammonia, nitrite, or rapid temperature changes can cause loss of appetite. Ensure the tank has adequate algae growth by checking lighting duration and intensity. If water quality is good and algae is present, offer supplemental vegetables and pellets. If the fish remains inactive or ill, it may need isolation in a hospital tank.

Are Siamese algae eaters safe with planted tanks?

Yes, they do not uproot or destroy plants. They graze on algae growing on leaves and stems without damaging the plants themselves. They are one of the safest algae-eating fish for planted setups, especially compared to plecos that can uproot and eat soft plants.