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Passport
- Family
- Tetras
- Grows to
- 3.5 cm (1.4")
- Lives
- 4–5 years
- Temperament
- Peaceful
- Care
- Intermediate
- Swims
- Mid-water
- Keep
- In a group of 8 or more
- Water
- 23–29 °C (73–84 °F)
Brazil
Care requirements
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On record for Cardinal Tetra: adult size, lifespan, minimum tank, temperature, ph, hardness, minimum group, diet, care level, swim level, tank length.
A figure that is not on record is left out rather than guessed. One marked Suggested comes from keeping knowledge rather than a page.
- Minimum tank 57 L / 15.0 US gal
- pH 3.5–7.5
- Hardness 1–12 dGH
- Diet omnivore
- Tank length 60 cm minimum
Care notes written from general aquarium knowledge, not from the cited sources.
About
Cardinals are what people buy once they've kept neons and want the same idea done properly. The red runs the whole length of the body instead of stopping at the middle, and against a dark tank the blue stripe above it reads almost like it's lit from inside.
Most of the ones you'll buy were caught wild in the Rio Negro, which is unusual now and worth knowing. It makes them fussier than a tank-bred neon about water quality, especially in their first weeks with you, and it means the fishery gives people along that river a living reason to leave the forest standing.
In the wild they rarely see a second year. Yours will, comfortably, so don't read too much into the short lifespans you'll find quoted from field studies.
Tank setup
Give your cardinals a dark floor and dim light, because everything about how they look depends on it. Over pale gravel under a bright lamp they wash out to a thin pink line; over sand and leaf litter under floating plants they turn into the fish you paid for.
Build the tank around wood, roots and dried leaves. They come from flooded forest streams full of exactly that, and the tannins those release suit them and tint the water the colour of weak tea, which is the point rather than a problem.
Soft, acidic water is what wild-caught fish want, and it's the single biggest difference between cardinals that thrive and cardinals that slowly fade. Tank-bred stock is far more forgiving.
Plant it heavily but leave swimming room through the middle. Cryptocorynes, java fern and anything else that tolerates low light will do the job.
Feeding
Cardinals eat almost anything small enough, and a good micro pellet or crushed flake covers the basics. What actually brings out the colour is live and frozen food — daphnia, moina, baby brine shrimp, small bloodworm — offered a few times a week rather than as a treat.
Watch the mouth. It's tiny, and anything they can't take in one go gets pushed around and then left to rot.
Avoid: big flake and anything sinking that they can't reach before it hits the substrate.
Filtration and flow
Keep the flow slow. These are backwater fish from streams that barely move in the dry season, and a strong current pushes them into a corner where you'll never see them properly.
Filter gently but change water properly. Wild cardinals are noticeably less tolerant of drifting nitrate than commercially bred fish, and the first sign is a group that has stopped feeding rather than anything you can see on their bodies.
An air-driven sponge filter suits them and won't shred fry if any survive.
With plants
Cardinals are completely safe with plants and look better among them than anywhere else. They don't dig, don't nibble and don't uproot.
Floating plants are the addition that matters most. Shade over the top calms them, darkens their colour and stops the surface glare that makes a shoal hang low and nervous.
Health
Wild stock arrives carrying more than tank-bred fish does, so quarantine cardinals if you can and expect a settling-in period. Losses in the first fortnight are common and losses after that are usually your fault rather than theirs.
Neon tetra disease turns up in cardinals as well, despite the name. You'll see a fish losing colour in patches, swimming oddly and wasting while the others stay fine. There's no cure, and the right move is to take that fish out early.
Colour is your gauge with this species. A shoal that dulls and stays dull is telling you something about the water before any test kit will.
Breeding
This one's difficult, and nobody manages it by accident. Cardinals need water far softer and more acidic than they need merely to live in, and outside that narrow window the eggs simply don't develop.
Set up a separate tank, keep it almost dark, and give them fine-leaved plants or a mesh floor to drop eggs through. The adults eat everything they lay, so take them out as soon as you see eggs.
Eggs and fry are both damaged by light, which is why so many attempts fail at the point everything looked fine. Keep the tank shaded and start the fry on infusoria before anything larger.
Tank mates
Avoid10
- Convict Cichlid Convict Cichlid grows to 15 cm against Cardinal Tetra at 4 cm, big enough to eat it.
- Jewel Cichlid Jewel Cichlid grows to 15 cm against Cardinal Tetra at 4 cm, big enough to eat it.
- Panda Garra Panda Garra grows to 9 cm against Cardinal Tetra at 4 cm, big enough to eat it.
- Pictus Catfish Pictus Catfish grows to 12 cm against Cardinal Tetra at 4 cm, big enough to eat it.
- Common Goldfish Common Goldfish is not safe with Cardinal Tetra: common goldfish and tetras are a bad pairing.
Only with care10
- Chinese Algae Eater Chinese Algae Eater is aggressive and Cardinal Tetra is peaceful.
- Cherry Barb Cardinal Tetra and Cherry Barb are an uneasy mix: barbs and tetras are a pairing to watch.
- Gold Barb Gold Barb is a risk to Cardinal Tetra: barbs and tetras are a pairing to watch.
- Odessa Barb Cardinal Tetra and Odessa Barb are an uneasy mix: barbs and tetras are a pairing to watch.
- Paradise Fish Paradise Fish is a risk to Cardinal Tetra: large gouramis and tetras are a pairing to watch.
No conflict is recorded with the other 85 species in the database, so nothing to flag. 3 species are not covered at all, so they could not be judged either way.