Betta fish care: the tank, the water, and the one-fish rule
A betta is sold in a cup and can live four years in a heated, filtered, planted 20-litre tank. What it actually needs, who it can live with, what to feed it, and the three problems every betta keeper meets.
The fish in the cup
A betta arrives in a plastic cup with an inch of water in it, and the shelf next to the cups sells vases, bowls and “betta kits” of two or three litres. Both are marketing, and both are why bettas have a reputation for dying in six months. A betta is a tropical fish from the warm, still, shaded waters of Thailand and Cambodia, with a labyrinth organ that lets it gulp air from the surface. That organ is why it survives the cup. It is not a reason to keep it in one.
Kept properly, a betta lives three to four years, learns who feeds it, builds bubble nests, flares at its reflection, and has more personality per gram than anything else in the hobby. Kept in a bowl on a windowsill, it lives a few cold months and dies of fin rot. The difference is the list below, and none of it is expensive.
What a betta needs, and none of it is a bowl
- ✓20 litres at least, 40 is better
- ✓Heater set to 25–27 °C, not optional
- ✓Gentle filter: sponge, or a baffled outflow
- ✓A lid, with an air gap at the surface
- ✓Broad leaves and a resting spot near the top
- ✓Dim, quiet, out of direct sun
- ✓One male. No other bettas, no fin-nippers
The tank
Twenty litres at the very least, and 40 is better. Small water swings in temperature and fouls in days; a 20-litre tank is the smallest that holds a heater and a filter and stays stable between water changes. A betta uses every centimetre of a 40-litre tank and is visibly happier in it.
A heater, set to 25 to 27 °C. This is the one that is not optional. Room temperature in most homes is 18 to 22 °C, which for a betta is a slow cold that shuts down its immune system and its appetite. Most “mystery” betta deaths in bowls are cold, and most fin rot starts there.
A gentle filter. Bettas come from still water and their long fins make them poor swimmers in a current. A sponge filter on an air pump is ideal; a hang-on-back filter needs its outflow baffled with a piece of sponge or a plastic bottle so the surface barely ripples. The filter is also where the bacteria live that keep the water safe, so the tank needs cycling before the fish goes in like any other.
A lid. Bettas jump, especially at night and especially when the water is wrong. Leave a gap for air at the surface, which they need.
Plants and places to rest. Broad-leaved plants like anubias, floating plants to dim the light, and a leaf or a small hammock near the surface. A betta rests, and a bare tank with nowhere to rest is a stressed betta. Skip plastic plants with sharp edges; long fins tear on them.
Dim, quiet, and away from the window. Direct sun means algae and temperature swings; a busy hallway means a fish that hides.
Water
The numbers are the same as any tropical tank, and the parameters guide has the detail: ammonia 0, nitrite 0, nitrate under 20 ppm, pH 6.5 to 7.5, a steady 25 to 27 °C. Bettas tolerate a range of hardness and pH; what they do not tolerate is change, so match temperature on every water change and never move a betta between waters in a hurry.
Change 25 % of the water every week, dechlorinated and temperature matched, the way the water-change guide describes. In a small tank that is a bucket and five minutes. Skip it for a month and nitrate climbs into the range where fin rot starts; skip it for three and the bowl reputation earns itself.
In the app — log the weekly test and the verdict tells you which readings are off for a tank this size, with the water change already sized to its volume, which in a 20-litre tank is one jug. The schedule keeps the weekly change and test on their day, and the tank’s health score on the home screen drops before the fins do.
Tankmates: the one-fish rule
One male betta per tank. No exceptions, and no “divided” tanks for a beginner. Two males will fight until one dies, and a male sees a female as a rival outside breeding. The fighting fish name is earned.
What else lives with a betta depends on the betta, and the honest answer is “often nothing, happily”. A 40-litre tank can add a group of six corydoras or kuhli loaches on the floor, which a betta mostly ignores, and nerite snails. Shrimp are a coin toss: some bettas ignore them, some eat every one.
What never does: anything that nips fins (tiger barbs, serpae tetras, most danios), anything colourful with flowing fins that a betta mistakes for a rival (guppies, especially male guppies, are the classic mistake), and gouramis, which are close relatives and get treated like one. A betta that is chasing, flaring constantly, or hiding with clamped fins in a community tank is telling you it needs its own.
Sororities, groups of females in a large planted tank, are real and can work. They are also a project for a keeper with a spare tank and a plan for when it does not work. Not the first betta.
In the app — Stocking ideas knows a betta is in the tank and will not suggest a fin-nipper or a gourami to share it; it suggests bottom dwellers and invertebrates that suit the volume, or says the tank is best left as it is.
Feeding
A betta is a carnivore with a stomach the size of its eye. Two to four betta pellets, once or twice a day, and that is a full meal. Frozen or live bloodworm, daphnia and brine shrimp twice a week are the treats that keep colour and appetite up. Flakes are a poor substitute: bettas ignore them until they sink and rot.
Skip one day a week. The most common betta problem after cold is overfeeding: a round belly, floating, then constipation and swim bladder trouble. A fast day and a cooked pea if it floats fixes most of it, and a betta that begs is not a betta that is hungry.
The three problems every betta keeper meets
Fin rot. Frayed, receding fins with a white or red edge, almost always in water that has been cold or dirty for a while. The fin rot guide is the plan: fix the water first, then the fins, with aquarium salt for a mild case. Nipped and torn fins from sharp decor look ragged but clean-edged and heal on their own in clean water.
Bloat and floating. Overfeeding, nearly always. Fast, pea, feed less. A betta that floats, is lethargic and has a swollen belly with scales that stand out is dropsy, which is a different and much more serious condition and needs a checkup today.
Lethargy and a lost appetite. Check the thermometer first: a betta at 20 °C lies on the bottom and stops eating. Then the test kit. Then, if both are right and the fish has a gold dusting under a torch, velvet, which bettas are prone to and which the ich guide’s treatment section covers.
Life with a betta
A betta learns the person who feeds it within a week and comes to the front of the tank for them. It builds bubble nests at the surface when it is content, which means the water is warm and clean, not that it needs a mate. It flares at a mirror for a minute a day happily and at a neighbouring betta all day miserably; if two tanks sit side by side, put a card between them. Glass surfing, pacing up and down the front glass, is a bored or stressed betta: more plants, less light, fewer neighbours.
In the app — a betta gets its own inhabitant profile with a portrait, notes, and every checkup and journal entry filed against it. Log its length now and then and the growth chart shows a young fish filling out; when it goes off its food, the follow-up check-in and Finley both know exactly which fish you mean.
Common questions
Can a betta live in a bowl?
It can survive one for a while, which is not the same thing. A bowl has no heater, so the fish sits at room temperature well below the 25 °C it needs, and no filter, so ammonia builds between water changes. Bettas in bowls die of cold and fin rot within months. A 20-litre tank with a heater and a sponge filter costs about the same as a decorative bowl and keeps the fish alive for years.
Do bettas need a heater?
Yes, everywhere except a room that is reliably 25 °C or warmer day and night, which is almost nowhere. A cold betta is lethargic, stops eating, and is the fish that gets fin rot. A small adjustable heater set to 25 to 27 °C is the single most important piece of equipment in the tank.
How long do betta fish live?
Three to four years in a heated, filtered, planted tank, and occasionally five. The fish in the shop is already six months to a year old, because it has to be adult to show its fins and colour. A betta that dies within a year of purchase almost always died of the tank, not of age.
Can two bettas live together?
Two males, never; they fight to the death. A male and a female, not outside a supervised breeding attempt. A group of females, a sorority, can work in a large, densely planted tank for an experienced keeper with a backup tank, and it fails often enough that it is not a beginner’s project. One betta per tank is the rule that has no exceptions.