A betta not eating is telling you something changed, and most of the likely causes are things you can check yourself today: water that is too cool, a water quality problem, a recent move or tank change, or the food itself. It can also be a sign of illness. The Merck Veterinary Manual lists "not eating" among the common signs of illness in fish, alongside lethargy. So check the temperature and test the water first. If he is also hiding, sluggish, breathing hard or looks different, or the water is fine and he still refuses food, contact an aquatic veterinarian.
If he has skipped a few days and you are wondering whether to worry yet, this page is for you. Panic causes more losses than the original problem, so we will go through it in order.
"Three Days Now. Should I Be Worried?"
I understand why people want a number of days. I am not going to give one, and here is why.
You will find pages quoting how long a betta can survive without food. That figure answers the wrong question. A healthy fish going without food is one situation. A fish that has stopped eating because his water is poisoning him, or because he is ill, is a completely different one, and the survival figure tells you nothing about which you have.
The useful question is not "how long can he go?" It is "why has he stopped?" Nearly everything that makes a betta refuse food also shows up somewhere else: on the thermometer, in a test kit result, or in how he looks and moves. That is where to look.
Merck's Common Signs of Illness in Fish (Merck Veterinary Manual, read September 25, 2026) puts "not eating" on the same list as lethargy, slow or rapid breathing, loss of color, spots, swelling or bloating, and floating or swimming in unusual positions. Not eating on its own is a reason to check. Not eating alongside anything else on that list is a reason to call.
Betta Not Eating: The Checks, In Order
Work through these in this order. The early ones are quick, cost nothing, and rule out the most common problems.
| Check | What you are looking for | What to do next |
|---|---|---|
| 1. Temperature | Water cooler than a betta's range | Correct it gradually with a working heater |
| 2. Water tests | Any ammonia or nitrite | Follow the ammonia or nitrite steps; water first, food second |
| 3. Recent changes | New tank, move, big water change, new tank mate | Keep things stable and watch |
| 4. The food | Old, new, too large, or piling up uneaten | Remove leftovers; check the food itself |
| 5. Other signs | Anything from the Merck list | Contact an aquatic veterinarian |
1. Check the temperature
Bettas are tropical fish. Dr. Krista Keller of the University of Illinois College of Veterinary Medicine gives a range of 76°F to 81°F for a betta tank, and RSPCA Australia gives 24 to 26°C (about 75 to 79°F). The University of Florida IFAS fact sheet on bettas says plainly that they "do not do well in cold water."
Read the thermometer, not the heater dial. Heaters fail, get unplugged, or cannot keep up when a room cools down at the change of season. If the water has dropped, bring it back up gradually rather than all at once. I explain why "tropical" is not one number on a separate page.
2. Test the water
A betta cannot tell you the water is bad, but a test kit can. Test at least for ammonia and nitrite. Any reading above zero on either one is a problem to fix before you think about food, and feeding more into that water only adds to it.
If ammonia is showing, start with my page on what to do first when ammonia reads above zero. If the tank is new, the Merck Veterinary Manual's pet owner page on fish disorders notes that new tank syndrome occurs "within the 1 to 3 weeks after a new system is set up." A betta that stops eating in a new tank is a strong reason to read about new tank syndrome symptoms.
3. Think about what changed
Go back over the last week or two. Did he move to a new tank or a new home? Was there a large water change, a deep clean, a new decoration or a new tank mate? Did the room get colder or noisier?
Any of these can put a fish off his food for a while. A betta that has just come home from the shop is the most common version of this, and many keepers see a new fish ignore food at first. That is not a reason to skip the other checks. A new betta can also be sick, and a new tank can also be uncycled. But if everything else checks out, stability helps more than intervention. Resist the urge to change several more things at once.
4. Look at the food itself
Before you blame the fish, look at what you are offering.
- Is food collecting on the bottom? If so, he may have been refusing it for longer than you realized. Remove it, because rotting food drives ammonia up.
- Did you switch foods recently? Fish can ignore an unfamiliar food.
- Is the pellet too large? A betta that takes food and spits it out may be dealing with a piece that is too big for him.
- How old is the container? Fish food that has been open a long time, or stored somewhere warm or damp, may not be what it was when you bought it.
Offering a small amount of a different suitable food, such as a frozen food he has eaten before, is a reasonable test. Offering more and more food until he eats something is not, because every uneaten piece ends up in his water.
5. Look for other signs
This is the check that decides whether to call a vet. Watch him for a few minutes and compare what you see with the Merck list. Is he sitting on the bottom or hiding all the time? Are his fins clamped against his body? Is he breathing faster than usual, or gasping at the surface? Has his color faded, or do you see spots, fuzz, swelling, raised scales or wounds?
RSPCA Australia's Knowledgebase article How should I care for my Siamese fighting fish? (last updated May 1, 2024, read September 25, 2026) lists fish that "sink or bob to the surface" and fish with "lumps, bumps, wounds, clamped fins" as showing poor health, and says a fish "constantly hiding or appearing lethargic and unresponsive to its owners is likely to be stressed or suffering illness and should be provided with appropriate veterinary care."
I will not try to tell you which illness matches which sign. A description is not enough to diagnose a fish, and guessing leads people to the wrong treatment.
What Not to Do While You Work It Out
A worried owner can make things worse without meaning to. These are the common ones.
- Do not keep adding food. It does not tempt a fish that is unwell. It rots and fouls the water.
- Do not reach for a medication without a diagnosis. Treating the wrong problem costs time and can harm the fish or the filter bacteria. Any medication decision belongs with a vet who has assessed him.
- Do not add salt or other additives "just in case." The right approach, if any, depends on what is actually wrong.
- Do not change everything at once. If you fix the temperature, do a water change and switch the food on the same day, you will never know what helped, and the combined change is itself a stress.
When to Contact an Aquatic Veterinarian
Contact a vet who treats fish, rather than continuing to wait, if:
- he is not eating and shows any other sign from the Merck list
- he is hiding constantly, lethargic, or unresponsive, which RSPCA Australia links to stress or illness
- the temperature and water tests are normal and he is still refusing food
- he is getting worse, or other fish in the tank are affected
Not every area has a fish vet nearby, and many people do not know they exist. My page on finding an aquatic veterinarian for fish explains when to call and how to find one. Have your recent test results and temperature readings written down before you phone, because they are the first things a vet can use.
Frequently Asked Questions
Why is my betta not eating but still swimming normally?
A betta can stop eating before he shows other changes. Check the water temperature, test for ammonia and nitrite, and think about recent changes to the tank or his food. If those are all fine and he still refuses food, or other signs appear, contact an aquatic veterinarian.
My new betta will not eat. Is that normal?
Many keepers see a new betta ignore food at first after a move. It is still worth checking the temperature and water, because a new fish can also be ill and a new tank may not be cycled.
Should I try a different food?
Offering a small amount of a different suitable food is a reasonable test. Remove anything he does not eat. Do not keep adding food, because uneaten food fouls the water.
Can cold water stop a betta from eating?
The University of Florida IFAS fact sheet says bettas "do not do well in cold water," and veterinary sources give a warm range for their tank. Check the thermometer early, and correct a low temperature gradually.
When is a betta not eating an emergency?
When it comes with other signs such as lethargy, constant hiding, fast breathing, spots, swelling or floating in unusual positions, or when he keeps refusing food after the water checks out. At that point, contact an aquatic veterinarian.