A betta refusing food is worrying and rarely urgent on the first day. Work through it in order, because the order is what saves time.
Work through it in this order
1. The water
Ammonia or nitrite above zero suppresses appetite, and it is the first thing to rule out because it is both the most likely and the most harmful.
If either is present, change 50 percent of the water, dechlorinated and temperature matched, and repeat daily until both read zero. Appetite often returns within a day or two of the water being right.
High nitrate has a similar but milder effect. Above roughly 20 ppm is worth correcting.
2. The temperature
A cold betta is a slow betta with a slow gut. Below about 23 °C appetite drops noticeably.
Check the thermometer, not the heater dial, since dials are frequently wrong by several degrees. If it is cold, bring it up gradually rather than all at once.
3. Recent changes
Ask what happened in the last week.
A new tank, a house move, a large water change, rearranged decor, a new tank mate or a new food can all produce a few days of refusal. This is settling rather than illness, and the response is to stop intervening: lights low, one small offering a day, remove what is not taken.
4. The food itself
Two common mechanical problems.
The pellet is too big or too hard, so the fish mouths it and spits it out. Soak it in tank water for a minute, or buy a smaller pellet.
The food is stale. An opened tub loses vitamins over months and bettas do notice. If it has been open since last year, that is a plausible cause on its own.
The useful test is a single thawed frozen bloodworm. Almost no healthy betta refuses one. If it takes that but not pellets, the problem is the pellets. If it refuses that too, move on.
5. Illness
Now look at the fish rather than the tank.
| Alongside not eating | Suggests |
|---|---|
| Clamped fins | Water quality, chilling or early infection |
| Swollen belly | Constipation, or dropsy if scales are raised |
| Sitting on the bottom | Cold, swim bladder problem, or age |
| White patches or fuzz | Fungal or parasitic infection |
| Laboured breathing or gasping | Nitrite, or gill problems. Test urgently |
| Bulging eye | Popeye, usually secondary to water quality |
| Nothing else at all | Often stress, food, or settling |
That last row is worth reading carefully. A fish with no other symptom, in water that tests clean, at the right temperature, is usually not ill.
How long you have
A healthy adult betta tolerates several days without food comfortably, and a week or more without lasting harm. Bettas evolved where meals were unpredictable.
That is not an argument for waiting. It is an argument for working through the list methodically instead of throwing three treatments at the tank on day two.
Where it becomes urgent: refusal beyond about two weeks, refusal alongside any of the symptoms in the table above, or visible weight loss with a sunken belly. Those are veterinary conversations.
What not to do
Do not keep dropping food in. Uneaten pellets rot into ammonia, which makes the original problem worse. Offer a small amount, wait a few minutes, remove what is left.
Do not medicate on the strength of not eating alone. It is a symptom shared by almost everything, including nothing at all, and medication in clean water is another stressor.
Do not change several things at once. If you alter the food, the temperature and the water on the same day, you will not know which one worked.
Do not assume the worst on day one. Settling and fussiness are far more common than disease.
Our limits here
We are keepers rather than veterinarians. This article is a process for ruling things out in a sensible order, not a diagnosis.
If your fish has not eaten for two weeks, is losing condition, or shows any of the symptoms listed above, contact an aquatic veterinarian.
Where to go next
Since water quality is the most common cause, the parameters guide is where to go if any of your readings looked wrong.