Betta fish care
Almost all of the work is in the first month. After that a planted five-gallon asks for about fifteen minutes a week, for years.
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The whole thing, in six lines
- Tank: 5 US gallons minimum, which holds about 4.3 gallons of water.
- Heat: 25W for that tank in a typical room, holding 78°F. The sum.
- Filter: gentle. About four turnovers an hour, and baffled if it is more.
- Cycle: three to six weeks, before the fish. Not skippable.
- Feed: two or three granules once a day. Its stomach is about the size of its eye.
- Change water: 25-50% weekly, temperature-matched, dechlorinated.
Everything below is the reasoning.
Temperature: the most commonly missed requirement
Aquarium Co-Op publishes that bettas prefer around 80°F, and that American rooms are commonly 67-69°F. That eleven-degree gap does not close on its own, and a betta living in it is lethargic, eats less and gets sick repeatedly - which is usually blamed on something else entirely.
We size heaters to hold 78°F rather than 80, so the heater has margin. The full range, and what happens at each end.
Water: what actually matters
Ammonia: 0. Nitrite: 0. Nitrate: under about 40 ppm. Those are the only readings that matter week to week, and the first two are absolute.
Ammonia comes from the fish and from uneaten food. Bacteria in the filter convert it to nitrite, then to nitrate. Nitrate accumulates and is removed by water changes and by plants. That is the whole system.
pH matters far less than people think, within reason. A stable pH of 7.6 is better than one that swings between 6.8 and 7.4 because you chased it with chemicals. Do not buy pH adjusters. Bettas adapt to a wide range; they do not adapt to a moving target.
The dosing, computed from published directions
Seachem publishes Prime at 5 mL per 50 US gallons of new water, and Stability at 5 mL per 10 US gallons on day one. Applied to nano volumes:
| Tank (rated) | Actual water | Prime, full volume | Prime, 50% change | Stability, day one |
|---|---|---|---|---|
| 3 US gal | 2.6 gal | 0.26 mL | 0.13 mL | 1.3 mL |
| 5 US gal | 4.3 gal | 0.43 mL | 0.22 mL | 2.15 mL |
| 10 US gal | 8.5 gal | 0.85 mL | 0.43 mL | 4.25 mL |
| 20 US gal | 17 gal | 1.7 mL | 0.85 mL | 8.5 mL |
Buy a 1 mL syringe. A capful in a 5-gallon is a ten-times overdose - Seachem states overdosing Prime is safe, so it will not hurt the fish, but you will empty a bottle in a month for no reason.
Feeding
Two or three granules once a day, or a slightly larger meal five days a week with two fasting days. A betta’s stomach is roughly the size of its eye, and everything uneaten becomes ammonia in a very small volume of water.
Overfeeding is the single most common husbandry error and it causes three problems at once: an ammonia load, constipation and bloating in the fish, and a pest snail population explosion if any are present.
A betta is an insectivore, which is why an insect-based food suits it better than a fish-meal-and-wheat pellet. Check the granule size too - a food the fish cannot physically get in its mouth is just ammonia on a delay.
The weekly routine, in full
25-50% water change. Temperature-matched - not “roughly right”, but checked with the same thermometer. Dechlorinated per the table above. A light siphon over the open substrate, not a deep dig. A wipe of the front glass.
Fifteen minutes, once a week. The schedule, including what to do monthly and what not to do at all.
Never rinse filter media under the tap
Chlorine kills the bacterial colony you spent a month growing, and the tank re-cycles from scratch with a fish in it. Filter media is rinsed in old tank water, in a bucket, when the flow visibly drops - every two or three months, not weekly.
This is a genuinely common way to lose a fish in month three, and it always looks like it came from nowhere.
What a healthy betta looks like
Fins spread rather than clamped. Active - patrolling the tank rather than sitting on the bottom all day. Color strong. Eating readily. Interested in you when you approach, which bettas genuinely are.
The two things worth watching for: a fish that suddenly stops eating, and a fish that sits on the bottom for a whole day. Both are non-specific and both warrant testing the water and checking the thermometer immediately, before anything else.
What we will not do on this site
Diagnose a sick fish, or recommend a medication. Diagnosis from a description is unreliable, most aquarium medications are sold with no dosing data for a four-gallon volume, and the difference between fin rot and mechanical fin damage is not something a website can establish.
Where a symptom has a clear environmental cause - and with bettas it very often does - we say so, because fixing the temperature or the ammonia is not treatment, it is removing the cause. Where it needs a diagnosis, we say that instead of selling you a bottle. That boundary is deliberate.
What we would buy for this
Chosen from the same registry as our roundups, on published specifications and the arithmetic they imply - not on testing we have not done.
Seachem Prime
The dechlorinator whose published dosing makes it the obvious nano choice: 5 mL treats 50 US gallons, so a 5-gallon water change needs half a milliliter. A 100 mL bottle is therefore roughly two hundred water changes. It also binds ammonia and nitrite, which is the property that turns a cycling accident into a survivable week.
Skip it if: You need something you can dose by the capful into a nano. At this concentration a capful in a 5-gallon is a ten-times overdose - you are measuring in drops.
Fluval P25 Submersible Heater, 25W
The default answer for a 5-gallon betta tank, and the reason the folk rule of thumb happens to land in the right place. Our sum for a 5-gallon in a normal US room - 68F, Aquarium Co-Op's published figure for a typical American house - is 15.1W. Nothing is sold at 15W. The next size up is 25, and that is the P25.
Skip it if: You want to run a degree cooler in summer or warmer for a sick fish. This is preset; buy the adjustable if you want a dial.
Fluval Bug Bites Betta Micro Granules
An insect-larvae-based granule sized for a betta's mouth, which is the specification that actually matters and the one most betta foods get wrong. A betta is an insectivore in the wild; a food built on black soldier fly larvae is closer to that than a food built on fish meal and wheat.
Skip it if: Your betta already refuses granules. Some individuals will only take a floating pellet, and a food the fish will not eat is just ammonia on a delay.
Frequently asked
How hard is it to keep a betta?
Front-loaded rather than hard. The first month - setting up and cycling - is where the work and the risk are. After that a properly set up five-gallon needs about fifteen minutes a week.
How often should I change the water in a betta tank?
25-50% weekly in a cycled, filtered tank. More often in an uncycled or unfiltered one - which is a holding pattern rather than a system. The full schedule.
Do I need to test the water forever?
Daily during cycling, weekly for the first couple of months, then monthly once the tank is established and stable - plus any time something looks wrong. The value is in the trend, so write the numbers down.
Why is my betta not eating?
Check the temperature and the water first, in that order - a cold betta’s digestion slows to almost nothing, and ammonia suppresses appetite. Both are far more common than illness and both are things you can fix today. If the water and temperature are right, that is a question for someone who can see the fish.
Can I use tap water for a betta tank?
Yes, dechlorinated. Seachem publishes Prime at 5 mL per 50 US gallons, so a 5-gallon needs about 0.43 mL. Never use untreated tap water - chlorine kills both the fish and the filter bacteria.