How do I keep my betta healthy?

What should I know about bettas at a glance?

Bettas (Betta splendens, the Siamese fighting fish) are small tropical fish from Southeast Asia, bred for their colors and long fins. They breathe air from the surface as well as through their gills, using a labyrinth organ that the University of Florida describes as an adaptation to shallow, warm water with little oxygen.

What health problems do vets see most in bettas?

The Merck Veterinary Manual says many fish diseases are the result of stress, poor water quality, overcrowding and failing to quarantine new fish. In a betta, these are the problems to know.

• Ammonia and nitrite poisoning: fish waste and leftover food make ammonia, which is highly toxic. Bacteria in the filter turn it into nitrite, also toxic, and then into nitrate, which is much less so, as the Merck Veterinary Manual explains. A new tank with fish in it before those bacteria grow can reach toxic levels in its first weeks, which vets call new tank syndrome.
• Ragged fins (fin rot): fins that look frayed or get shorter week by week. Merck lists ragged fins, bloody spots and ulcers among the signs of Aeromonas, the most common bacterial infection of freshwater aquarium fish, and notes that a laboratory test shows which antibiotic will work.
• White spot (ich): white dots on the skin and fins from a parasite. One parasite can produce hundreds of new ones, which is what makes it so deadly, and the treatment is timed by the water temperature, so Merck recommends advice from a fish health professional.
• Velvet: a fine yellowish dust, smaller and harder to see than white spot, sometimes a velvety film on the skin, with loss of appetite, lethargy and rubbing against objects. Merck notes that high death rates are common.
• Dropsy: a swollen body with scales sticking out like a pinecone. Fish vet Jessie Sanders explains on PetMD that it is a sign of an underlying problem, most often chronic stress from poor water, and that severe cases are often fatal.
• Swim bladder problems: a fish that floats, sinks or swims abnormally because it can't control its buoyancy. PetMD calls poor water quality one of the most common and overlooked causes, lists improper feeding and infection among the others, and says an X-ray is the best way for a vet to check the swim bladder.
• Gut parasites: Merck names bettas among the fish whose intestines Spironucleus and Hexamita attack, causing lethargy, weight loss and white, stringy droppings. Shipping, crowding, handling and stress can trigger them.
• Tumors: Merck describes a tumor occasionally seen in bettas, the iridophoroma, a soft mass on the outside that often invades the tissue and organs around it. In Brazil, a team at the UFRPE veterinary teaching hospital removed two skin tumors from a betta's fin in 2026, as Compre Rural reported.

Do bettas need vaccines or medicines?

No vaccine is given to pet bettas. The Merck Veterinary Manual notes that vaccines are used in large fish farms and are still uncommon for pet fish. Prevention is the water, the food and keeping new fish apart.

• Medicines only with a diagnosis: the University of Florida advises ruling out the water, the diet and infections first, because many drugs and chemicals do more harm than good when used wrongly.
• Antibiotics: Merck says antibiotics in the water aren't usually recommended, because they tend to kill the filter's bacteria. Ask the vet how to watch ammonia and nitrite while you treat.
• Finding a fish vet: ask your usual vet, who may see fish or know a colleague who does, as the University of Florida suggests. In the United States, the American Association of Fish Veterinarians has a vet locator. In Brazil, university veterinary hospitals can see fish, like UFRPE's in Pernambuco.

How big a tank does a betta need, and does it need a heater?

It depends on who you ask. OATA asks for at least 20 liters for one male, with a filter and a heater whatever the size. RSPCA Australia says 20 liters or more, and 10 at the very least. PetMD gives 2.5 gallons (about 9.5 liters) as the minimum and 10 gallons (about 38 liters) or more as ideal.

Two studies in Animal Welfare looked at how bettas behave by tank size. In a 2024 study, bettas swam more and showed less abnormal behavior in a 19.3 liter tank than in containers of 1.5 to 5.6 liters, and the authors recommend tanks larger than 5.6 liters at home, with gravel, live plants and places to hide. Another found at least 10 liters were needed for the fish to swim normally.

On the other side, the University of Florida argues that bettas evolved in shallow, warm water and can do well in small tanks and bowls when the water is well managed. The Merck Veterinary Manual agrees that a small betta tank may need no filter or heater, but then needs larger, more frequent water changes, perhaps as much as 50% a week. Ask your vet what suits your home and your fish.

• Heater: a submersible aquarium heater, as RSPCA Australia advises, because room temperature is too cold and changes through the day. The University of Florida says a betta in an unheated container needs a room that never drops below 22 °C.
• Thermometer: keep a separate thermometer in the tank, because the heater's own setting isn't proof of the water's temperature, as the Merck Veterinary Manual notes.
• Gentle filter: bettas prefer calm water. RSPCA Australia asks for a filter with adjustable flow, and PetMD suggests air-driven sponge filters or other low flow filters.
• Lid with an air gap: bettas can jump, so use a lid, but leave space between the water and the lid so the fish can breathe air, as RSPCA Australia advises.
• Plants and hiding places: live plants, or plastic plants and caves without sharp or rough edges that could tear long fins, as OATA suggests.
• Where it stands: out of direct sunlight, which warms the water and lowers its oxygen, according to the Merck Veterinary Manual. Lights should go off at night, because a light left on all the time stresses fish.

How do I keep a betta's water clean?

Set the tank up weeks before the fish arrives, test the water and change part of it every week. A betta can't get away from its water, so the water is its health.

• Cycling a new tank: the filter needs time to grow the bacteria that clear ammonia and nitrite. PetMD plans 4 to 6 weeks, and the Merck Veterinary Manual says it can take up to 8 weeks in a tropical tank. Ask your fish shop or vet how to cycle yours before adding the fish.
• Water tests: RSPCA Australia tests ammonia and nitrite every 2 to 3 days for the first 6 weeks, then every 1 to 2 weeks. Its targets are ammonia under 0.1 ppm, nitrite under 0.2 ppm, nitrate under 50 ppm and pH 6.5 to 7.5. OATA accepts pH 6.0 to 8.0 and tests every week.
• Partial water changes: 25% every week for OATA, 10 to 25% for RSPCA Australia, with a gravel clean. Smaller tanks without a filter need more, as the Merck Veterinary Manual notes.
• Dechlorinator: tap water usually carries chlorine or chloramine, both toxic to fish and to the filter's bacteria. The Merck Veterinary Manual says to treat all new water with a dechlorinator before it goes in the tank.
• When ammonia is high: in a new tank with total ammonia at 2 mg/L or more, the Merck Veterinary Manual advises changing at least half the water, and testing often, sometimes daily, until ammonia and then nitrite fall.

Which signs in a betta can't wait?

Emergency care for fish isn't as easy to find as it is for dogs and cats, as the Merck Veterinary Manual notes, so act early. Test the water first and call a vet who sees fish if you see any of these.

• Hiding all the time, staying in one corner for a long time, or not reacting to you: RSPCA Australia lists these, with lethargy and clamped fins, among the signs of a stressed or sick fish. A betta that stops eating belongs on the same list.
• Floating, sinking or swimming on its side: check the water and the heater now. PetMD puts testing the water as the first step.
• A swollen body or scales sticking out: dropsy can progress quickly. PetMD says recognizing it early and getting veterinary care is critical.
• White dots, gold dust or a velvety film: white spot multiplies fast and velvet often kills, as Merck warns.
• Gulping at the surface far more than usual, or rubbing against objects: bettas breathe air, but constant gulping and scratching are signs of skin and gill parasites in Merck. Test the water now.
• Fins shrinking, bloody spots, sores or lumps: signs of an infection or a growth. RSPCA Australia counts lumps, bumps and wounds among the signs of poor health.
• Ammonia or nitrite on a test, or a heater that failed: the Merck Veterinary Manual notes that water tests can catch toxins like ammonia and nitrite before they become fatal. Change part of the water today, check the heater and test again.

Find a vet who sees fish before you need one. Don't add medicines to the tank without a diagnosis.

How do I care for a betta day to day?

Feed little, keep the water warm and steady, and let your betta live alone. Overfeeding is the easiest mistake to make, and the Merck Veterinary Manual notes that it leads to health problems as well as a dirty tank.

• Food: once a day, only what your betta eats in under two minutes, as RSPCA Australia advises, with betta pellets or granules and occasional frozen treats such as brine shrimp or daphnia. PetMD suggests a portion about the size of the fish's eye and removing what's left.
• Males alone: two males should never share a tank, according to OATA. They fight, biting each other's fins and sides, as the University of Florida describes.
• Tank mates: a male can share a tank only with very calm fish, as OATA puts it. PetMD suggests corydoras, snails or shrimp and warns against fin nippers like tiger barbs, and RSPCA Australia wants at least 40 liters for a shared tank.
• New fish: keep any new tank mate in a separate tank first. The Merck Veterinary Manual advises 30 to 60 days of quarantine for valuable pet fish.
• Mirrors: RSPCA Australia says mirrors should never be left in a tank, because a male may flare at his reflection over and over, which causes stress and exhaustion.
• Hands: wash them after working in the tank. The Merck Veterinary Manual notes that fish mycobacteria can cause skin infections in people.

How do I keep my betta's health record?

VetVitae, a pet health record app, keeps your betta as one fish with its tank volume, and logs water tests with temperature, pH, ammonia, nitrite, nitrate, GH and KH. It warns while ammonia or nitrite are above zero, and when nitrate goes above 50 mg/L.

It also logs tank care with how much water you changed, medicines dosed by the water in the tank, and vet visits, and suggests betta routines like Feed and Check the tank. See aquarium records. VetVitae is free on iPhone, Android and the web.

This guide is general information, not veterinary advice. Your vet knows your pet.

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