Cardinal Tetra Care: Tank Size, Schooling & Diet
Cardinal tetra care guide: keep a school of six or more in a 15 to 20 gallon tank, warm soft acidic water at 73 to 81F, plus diet, tankmates, and health tips.
Cardinal tetras are the brighter, slightly larger cousins of the neon tetra, with a vivid red stripe running the full length of the body. Keep them in a tank of at least 15 to 20 gallons in a school of six or more, ideally ten or more, at 73 to 81F in soft, acidic water. They are peaceful and, with good care, longer lived than neons. They handle warmth better than neon tetras, which makes them a standout in warm planted community tanks.
This guide covers the right school size, tank setup, the warm soft acidic blackwater cardinals love, diet, tankmates, and health. Plan your build with the minimum tank size calculator, confirm real water volume with the aquarium volume calculator, and fit your school sensibly with the stocking calculator.
Cardinal tetra care at a glance
| Care factor | Detail |
|---|---|
| Minimum tank size | 15 to 20 gallons |
| Adult size | About 1.25 to 2 inches |
| Temperature | 73 to 81F (warmer than neon tetras) |
| pH | 5.5 to 7.0 (soft, acidic) |
| Hardness | Soft, roughly 1 to 8 dGH |
| Diet | Omnivore: micro pellets and small flakes plus tiny protein treats |
| Temperament | Peaceful and shy |
| Lifespan | About 3 to 5 years |
| Grouping | Schooling: keep 6 or more, ideally 10+ |
Tank setup
Cardinals need room for a proper school, so plan for at least 15 to 20 gallons and choose a longer tank that gives the group space to shoal. They come from shaded, plant rich Amazon blackwater, so they look and behave best in a densely planted tank with driftwood, subdued lighting, and dark substrate. That setup brings out the full intensity of their red and blue and helps these somewhat shy fish feel secure enough to swim in the open. Bare, brightly lit tanks make cardinals nervous and washed out.
Heater, filter, and cycling
Cardinals are warmth loving, so use a small adjustable heater to hold 73 to 81F, toward the warmer end if you keep them with discus. Pair it with a gentle filter, since these small fish dislike strong current. Never add cardinals to an uncycled tank. Complete the nitrogen cycle over about 4 to 6 weeks to establish beneficial bacteria before they arrive, and add them only after the tank has matured, since these sensitive fish suffer badly from new tank syndrome.
Water parameters
Cardinal tetras want soft, acidic, warm water, so target 73 to 81F, a pH around 5.5 to 7.0, and soft water. Because many cardinals are still wild caught, they especially appreciate blackwater conditions and a slow, careful acclimation. Driftwood, leaf litter, and botanicals such as Indian almond leaves release tannins that tint the water and gently lower pH, mimicking their native streams. Stability beats chasing a number, so hold conditions steady, test for ammonia, nitrite, and nitrate, keep ammonia and nitrite at 0 ppm, and control nitrate with regular partial water changes. If your tap water is hard, see our GH and KH guide.
Diet
Cardinals are omnivores with small mouths, so the staple should be a micro pellet or finely crushed flake they can actually swallow. Supplement several times a week with small frozen or freeze dried foods like daphnia, cyclops, and baby brine shrimp, which deepen their color and keep them in top condition. Feed small portions once or twice a day, only what the school clears in a couple of minutes, since excess food spoils the soft water cardinals are sensitive to.
Cardinal tetra tank essentials
Tetra TetraMin Tropical Flakes
$13.97 on Amazon
Balanced daily staple; crush lightly to suit small tetra mouths.
$13.96 on Amazon
Tiny pellets sized for the small mouths of cardinal tetras.
SunGrow Indian Almond (Catappa) Leaves
$5.97 on Amazon
Botanicals that add tannins and gently soften and acidify the water.
GREEN WATER FARM Indian Almond Leaf Powder
$15.99 on Amazon
Concentrated tannin source for recreating blackwater conditions.
Tankmates
Cardinal tetras are peaceful and ideal for warm, calm community tanks. Excellent companions include other cardinals and neon tetras, harlequin rasboras, corydoras catfish, kuhli loaches, peaceful gouramis, and dwarf shrimp in well planted tanks. Because they tolerate warmth, cardinals are also a classic dither fish for discus and German blue rams. Avoid large or aggressive fish that will eat them and avoid fin nippers like tiger barbs. As a school plus tankmates adds up quickly, confirm your numbers with the stocking calculator.
Common problems and health
Most cardinal tetra health issues come from unstable or poor water quality and from the stress of a new tank, so a water test is always the first step. Ich shows as white spots and is treatable with prompt action and stable warmth. Fin rot and faded color usually follow stress or dirty water. Because many cardinals are wild caught, they can arrive carrying parasites or stressed from shipping, so buy from a reputable source, acclimate slowly, and quarantine new arrivals when you can. Cardinals are generally a bit hardier and longer lived than neons once settled. For persistent illness, consult a local fish store or aquatic vet, since this guide is educational only.
Breeding
Cardinal tetras are difficult to breed in home aquariums and most for sale are either wild caught or commercially farmed. Successful breeding requires very soft, acidic blackwater, dim conditions, and a dedicated breeding tank, since the adults eat the eggs and the fry are tiny and light sensitive. For nearly all keepers, the goal is a vibrant, healthy school rather than raising fry, which is an advanced project.
The bottom line
Cardinal tetras deliver the most brilliant red and blue in the nano fish world when you give them what they need: a school of six or more in a planted, cycled tank of 15 to 20 gallons, warm soft acidic water at 73 to 81F, and peaceful tankmates. Let the tank mature, lean into blackwater conditions, and a cardinal school becomes a glowing, long lasting centerpiece. Plan it with our minimum tank size calculator, aquarium volume calculator, and stocking calculator.
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Frequently Asked Questions
What is the difference between a cardinal tetra and a neon tetra?
The clearest difference is the red stripe. A cardinal tetra has a vivid red line running the entire length of its body from nose to tail, while a neon tetra has red only on the back half. Cardinals are also slightly larger and prefer slightly warmer water. Many keepers find cardinals more brilliant and they tend to hold up better in warm planted tanks, though they usually cost a little more.
How many cardinal tetras should I keep?
Cardinal tetras are schooling fish and should be kept in a group of at least six, with ten or more producing a much better display and calmer fish. A larger school lets them shoal naturally, shows off their full color, and reduces stress. In small numbers they hide and lose color. Plan your tank and tankmates around a proper sized school using a stocking calculator.
What water conditions do cardinal tetras need?
Cardinal tetras come from warm Amazon blackwater, so they prefer 73 to 81F, a soft and acidic pH around 5.5 to 7.0, and soft water. They handle warmth better than neon tetras, which makes them a good fit for warm planted community tanks and even discus setups. As with all sensitive fish, a fully cycled, stable tank matters more than chasing an exact pH reading.
Are cardinal tetras hard to keep?
Cardinal tetras are moderately easy once your tank is mature and stable, but they are sensitive to poor water quality and to being added to a new, uncycled tank. Many are still wild caught, so they benefit from soft, slightly acidic water and a careful, gradual acclimation. Give them an established tank, a proper school, and good water, and they are hardy and long lasting.
How long do cardinal tetras live?
With good care, cardinal tetras commonly live around 3 to 5 years, which is notably longer than the 2 to 3 years typical of neon tetras. Their lifespan depends on stable, soft, slightly acidic water, a stress free tank with a proper school, and a varied diet. Quarantining new fish and avoiding water quality swings go a long way toward helping them reach their full lifespan.
What do cardinal tetras eat?
Cardinal tetras are omnivores with small mouths, so feed a quality micro pellet or finely crushed flake as the staple, supplemented with small frozen or freeze dried foods like daphnia, cyclops, and baby brine shrimp. Variety brings out their red and blue color. Feed small amounts once or twice a day, only what the school finishes in a couple of minutes, to keep their soft water clean.
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