First of all: test the water
Most Betta illnesses come from polluted or cold water.
First steps
- ✓Check the temperature: 25 to 28 °C
- ✓Test ammonia (NH₃) and nitrite (NO₂): both must be 0
- ✓Test nitrate (NO₃): under 20 mg/L
- ✓Change 30% of the water, at the same temperature
- ✓Write down the symptoms day by day
When to isolate the fish?
As soon as a fish shares its tank and shows a contagious disease (white spots, velvet, columnaris), or when a treatment could harm the plants, shrimp or snails in the main tank.
A Betta living alone can often be treated in its own tank, after removing any activated carbon from the filter.
Find by symptom
The most likely causes, and what to do first.
White spots like grains of salt
Likely causes
Ich (white spot disease), a parasite often triggered by a chill or stress.
What to do
Slowly raise to 28–30 °C, use a commercial anti-parasite treatment for 7 to 10 days, vacuum the substrate daily.
Fine gold or rust-coloured dust
UrgentLikely causes
Velvet (Oodinium), a parasite best seen with a torch in a dark room.
What to do
Total darkness for several days, 28 °C, velvet treatment as per the label. Act fast: it spreads quickly.
Frayed fins with blackened or whitish edges
Likely causes
Fin rot: bacteria taking advantage of poor water quality.
What to do
Test the water and change 30% every two days. If the fins keep receding despite perfect water: antibacterial treatment in a hospital tank.
Torn fins with clean edges
Likely causes
The Betta is biting its own tail (stress, boredom, bare tank) or got hurt on sharp décor.
What to do
Add plants and hiding places, remove any rough décor (tights test: if it snags, it tears). Fins grow back within weeks in clean water.
Swollen belly, normal scales
Likely causes
Most often constipation caused by overfeeding or very dry pellets.
What to do
Two to three days of fasting, then smaller, more varied meals (frozen and live food).
Swollen belly, scales raised like a pine cone
UrgentLikely causes
Dropsy: a sign of internal organ failure (often the kidneys), usually linked to an infection.
What to do
Isolate in a hospital tank at once and ask a vet for advice. The outlook is poor: check the water the other fish live in too.
Swims sideways, floats or stays sunk
Likely causes
Swim bladder disorder: overfeeding, constipation, cold water or infection.
What to do
Fast for two to three days, keep a steady 27 °C, and use a low water level in a hospital tank so it reaches the surface easily.
One or both eyes bulging
Likely causes
Popeye: one eye suggests an injury, both eyes a bacterial infection linked to water quality.
What to do
Spotless water and regular water changes. If the eye still swells after a week: antibacterial treatment.
Cotton-like tufts or whitish patches
UrgentLikely causes
A fungus on a wound, or columnaris, a bacterium that forms patches and spreads very fast.
What to do
Hospital tank and antifungal treatment for fungus. For patches that spread within hours, antibacterial treatment without delay.
Breathes fast, stays at the surface
UrgentLikely causes
Ammonia or nitrite in the water, water too warm, or gill parasites.
What to do
Test the water straight away and change 30 to 50% of it, at the same temperature, treated with dechlorinator.
Stays on the bottom, fins clamped, eats little
Likely causes
A general sign of discomfort: water too cold or polluted, stress, or an illness starting.
What to do
Check the heater (25–28 °C) and the water tests, then watch for two or three days for any other symptom.
Horizontal stripes on the body
Likely causes
"Stress stripes", common after transport or a change. In females, vertical bars instead show she is ready to spawn.
What to do
Nothing urgent: calm, soft light, hiding places. The stripes fade within a few days.
📋 Detailed sheets on common diseases
The hospital tank
A small separate tank, to treat a fish without risk to the others.
Setting it up
- ✓10 to 20 L tank with a lid
- ✓Heater set like the main tank
- ✓Gentle sponge filter, or no filter and daily water changes
- ✓No substrate, one smooth hiding place and a floating plant
- ✓Water from the main tank, to avoid a shock
During treatment
- ✓Follow the medicine's label exactly
- ✓Remove activated carbon, which absorbs treatments
- ✓Dim light, quiet surroundings
- ✓Feed lightly, remove leftovers
- ✓Continue a few days after the symptoms disappear
Prevention is better than cure
Stable water
Regular water changes, a reliable heater and a cycled tank: the best protection there is.
Measured feeding
Small, varied portions, with one fasting day a week.
Quarantine
Two to four weeks apart for any new fish before it joins others.