Should I buy it?
Cardinal Tetra
Paracheirodon axelrodi
Also known as: cardinal, large neon (trade)
More demanding than neons. They need soft, acidic water in a settled tank three months old or more. The colour repays the wait.
Cardinal Tetra tank mates · 60L tank size hub
peaceful · intermediate care
Sources & confidencehigh · verified · beginner: good
Checked against several solid care sources that mostly agree. Numbers here are a careful starting point. Your tap water, tank size, and habits decide the rest. How we evaluate.
Best for: Aquarists with soft water (RO mix, rainwater, or naturally low TDS) running a planted, mature community tank.
Avoid if: Your tap water is hard and alkaline, the tank is under three months old, or your stock includes larger predators.
Common mistakeKeeping small cardinal groups in hard or bright water is how keepers invent faded fish that 'never looked like the shop.' They need soft, dimmer conditions and a real school. Token numbers in a hard community kit are the wrong ownership plan.
Top things that go wrong
- Group welfare — not a solo display fish. Plan at least **6** together for normal behaviour; smaller groups often mean stress, colour loss, or nipping depending on species.
- Specialist husbandry. Ten or more for the colour to settle. Six is the absolute floor. Below that they wash out and hide.
- Shrimp & snails. Cherry shrimp and other dwarfs can coexist with peaceful small fish; baby shrimp are food for almost anything that finds them.
What most shops don't tell you
- 1.Myth: cardinal tetras thrive as a small handful in any hard bright community tank like hardy livebearers. Reality: they need soft, dimmer water and a real school — hard bright kits and token numbers wash them out and leave them hiding.
- 2.Keeping only three or four cardinals in a small bright tank. They lose colour and hide, especially in harder water.
- 3.Mixing with mollies, swordtails, or hard-water African cichlids without a split-tank or compromise plan.
- 4.More sensitive than neons. They want a tank that has been running three months or more, with soft acidic water that does not drift week to week.
About this species
Similar to the neon tetra but the red stripe runs the full body length. Cardinals are soft-water Rio Negro fish, fussier than neons about parameters.
- Beckford Pencilfish60L min · same group, comparable tank size
- Black Neon Tetra60L min · same group, comparable tank size
- Bloodfin tetra60L min · same group, comparable tank size
- Glowlight Tetra60L min · same group, comparable tank size
- Green neon tetra60L min · same group, comparable tank size
- Lemon Tetra60L min · same group, comparable tank size
- Silver Tip Tetra60L min · same group, comparable tank size
- X-ray tetra60L min · same group, comparable tank size
- Adolfoi coryalso intermediate peaceful, similar tank size
- Bamboo Shrimpalso intermediate peaceful, similar tank size
- Black ruby barbalso intermediate peaceful, similar tank size
- Brown / hockey-stick pencilfishalso intermediate peaceful, similar tank size
- Celebes Rainbowfishalso intermediate peaceful, similar tank size
- Celestial Pearl Danioalso intermediate peaceful, similar tank size
- Beckford Pencilfish tank mateslists this fish as a safe and recommended mate
- Checkerboard cichlid tank mateslists this fish as a safe and recommended mate
- Marbled Hatchetfish tank mateslists this fish as a safe and recommended mate
- Rosy Tetra tank mateslists this fish as a safe and recommended mate
- Rummy Nose Tetra tank mateslists this fish as a safe and recommended mate
- Sterba's Corydoras tank mateslists this fish as a safe and recommended mate
Plan grid
Key limits are above. Here: pH band, swim level, bioload, and activity.
Swim zones
Care snapshot
Quick compare before you buy. Not a score of how “good” the fish is.
- Beginner ease59
- Peacefulness90
- Community fit79
- Small-tank fit100
- Hardiness57
- Energy54
Numbers are deterministic planning indices from Fishori fields — not a scientific score of your individual fish.
Example setups
Starting points only. Run the pair checker for every fish you add.
Rough 90L+ layout: one calm centrepiece, 8–12 small tetras/rasboras, 6–8 corydoras-type bottom fish — verify every name in the pair checker before buying.
Safer directions include: Corydoras Catfish, Dwarf Gourami, Harlequin Rasbora.
Prioritise 6+ of Cardinal Tetra in 60L+ with filtration sized for messy feeding — add only mates that already pass pair checks with this species.
Compatibility
Tank mates for Cardinal Tetra
Usually safer (engine GOOD): Corydoras Catfish, Dwarf Gourami, Harlequin Rasbora. Conditional (CAUTION — read the pair page before buying): Angelfish, Tiger Barb. Avoid (RISKY): Jack Dempsey, Oscar. Every name links to a live pair check — the lists are a shortlist, not a stocking plan.
Usually safer
Open a pair page with this fish as the starting point.
Needs planning
Read the blocking rule on each pair page before experimenting.
Usually avoid
Do-not-stock combinations on conservative hobby rules.
Compare with
Run a real pair check: Cardinal Tetra + Corydoras Catfish
Behaviour and temperament
Cardinal tetras are peaceful schoolers that stay calmer in groups of six or more in soft water. They do not bully robust neighbours at all. Stress shows as fading, hiding, and losses when chemistry stays hard or predators share the same glass.
What sets them off
- Sudden crowding
- Poor water quality
Fin nipping: Not a habitual fin-nipper; stressed or crowded individuals can still test fins.
Predation: Not a predator toward similarly sized community fish; fry and dwarf shrimp are still fair game for most species.
Territory: Not strongly territorial, but still needs room so its working space does not overlap the next fish.
Planted tanks: excellent — easy plant ideas
In the glass: typical and warning signs
- Six or more hold midwater as a blue-and-red ribbon in soft planted water.
- Tight schooling after a fright is normal — give plants and length to reform.
- Faded colour in hard bright tanks usually means chemistry and light first.
- A scattered handful needs more of their own kind before a different staple.
- Low listed risk as aggressors.
- Angels, barbs, and large cichlids are the usual failure modes — not cardinal malice.
- Fix soft-water and school size before chasing mystery disease only.
- Remove predators and nippers at the first disappearance or tear.
Fish behaviour can vary between individuals and tank setups. Always observe new fish closely after introduction.
Water, food, and grouping
Hardness
soft
Diet
omnivore
Cardinal tetras are midwater omnivores that take micro-pellets, flake, and frozen foods in a school of six or more — more looks better — in soft, dimmer water. Hard bright community kits fade them even when the bowl looks full. Feed where the school holds among plants, and keep numbers honest so colour reads as a ribbon, not scattered sparks.
Shrimp & snails
Cherry shrimp and other dwarfs can coexist with peaceful small fish; baby shrimp are food for almost anything that finds them.
Ten or more for the colour to settle. Six is the absolute floor. Below that they wash out and hide.
- Hold 23 to 27 °C steadily on a real thermometer, not the dial on the heater.
- Aim for pH 5.5 to 7 and a hardness you can re-test in two weeks. A one-time strip in the shop car park is not a water test.
- Schooling species. Buy 6 or more from the same tank on the same day before adding any centrepiece fish.
- Tank volume meets or exceeds 60L published minimum for adults.
- You can stock at least 6 individuals (group welfare).
- Heater can hold 23–27°C without cooking cooler-water tank mates.
Explore and stocking hubs
Tank-mates hub, matching guides, category peers, and litre stocking lists around this species’ minimum tank.
Plan with tools
Check mates as pairs first, then add this fish in the tank builder for the full stocking.
Filtration & heating
A 60L minimum tank needs a filter rated for at least 240L/hr turnover and a heater to hold 23–27°C reliably.
Plant suggestions
Cardinal Tetra does well in planted tanks. Plants compatible with 23–27°C and pH 5.5–7:
Research: verified · Confidence: high · 4 linked source(s). We do not invent citations.
How Fishori evaluates compatibility (same logic as pair and tank tools).
- Seriously Fish. Paracheirodon axelrodi
Primary: aquarium size, water chemistry, behaviour, and compatibility (URL verified in upgrade script; recheck if site content changes).
- FishBase. Paracheirodon axelrodi
Secondary: taxonomy, distribution, and maximum length in nature; cross-check with aquarium import lines and measured tank parameters.
- Wikipedia. Paracheirodon axelrodi
Secondary: general species context; verify all husbandry numbers against a dedicated aquarium care sheet and your test kit, not a single table row.
- Wikipedia. Paracheirodon axelrodi (cardinal tetra)
Encyclopaedia overview; use specialist aquarium sources for your stock's real temperature/pH/footprint needs.
Evidence notes
- The Seriously Fish profile for the binomial in this record was successfully reached as the primary aquarium reference.
- FishBase contributes natural-range size and habitat context. Translate those numbers through your heater, your water report, and your tank footprint before stocking.
- Wikipedia is only cited if the article URL returned OK. Use it for orientation, not as the only care sheet for an import.
- All compatibility text reflects typical hobby experience and the Fishori model. Individual fish, shop stress, and the order tank mates are added in can still defy a single-paragraph label.
Featured compatibility checks
Curated pair pages for Cardinal Tetra. Each opens a full verdict — not just a list label.
- Cardinal Tetra + Neon Tetra
- Cardinal Tetra + Corydoras Catfish
- Cardinal Tetra + German Blue Ram
- Cardinal Tetra + Discus
- Cardinal Tetra + Dwarf Gourami
- Cardinal Tetra + Harlequin Rasbora
- Cardinal Tetra + Rummy Nose Tetra
- Cardinal Tetra + Oscar
- Cardinal Tetra + Apistogramma Borellii
- Cardinal Tetra + Apistogramma Macmasteri
- Cardinal Tetra + Apistogramma Trifasciata
- Cardinal Tetra + Marbled Hatchetfish
Common questions about Cardinal Tetra
- How big do Cardinal Tetra get?
- Around 4-5cm at adulthood. Slightly larger than neons but still in the prey class for any fish over 10cm with a gulp-and-swallow strike.
- What size tank does Cardinal Tetra need?
- 75L+ is realistic. The school needs lateral length to spread, and the extra volume buffers the parameter swings cardinals do not tolerate.
- Are Cardinal Tetra aggressive?
- Cardinal tetras are peaceful schoolers that stay calmer in groups of six or more in soft water. They do not bully robust neighbours at all. Stress shows as fading, hiding, and losses when chemistry stays hard or predators share the same glass.
- Do Cardinal Tetra need to be kept in a group?
- Ten or more for the colour to settle. Six is the absolute floor. Below that they wash out and hide.
- What is the most common mistake with Cardinal Tetra?
- Keeping small cardinal groups in hard or bright water is how keepers invent faded fish that 'never looked like the shop.' They need soft, dimmer conditions and a real school. Token numbers in a hard community kit are the wrong ownership plan.
- What fish can live with Cardinal Tetra?
- The Cardinal Tetra profile lists Corydoras Catfish, Dwarf Gourami, Harlequin Rasbora among its safer pairings (engine-checked GOOD). Angelfish, Tiger Barb are conditional (CAUTION): workable only with the specific conditions on each pair page. Avoid Jack Dempsey, Oscar (RISKY). Run the pair checker for your exact water and tank size before stocking.