Cardinal tetras are iconic schooling fish prized for their bright red-and-blue stripe and calm community temperament. They do best in a mature, cycled aquarium with stable water quality and low nitrates, and they show the best color in planted or lightly “blackwater” style tanks with shaded areas. Keep them in a proper school (8–12+), provide gentle-to-moderate filtration, and feed small high-quality foods with occasional frozen/live treats. In the right setup, a school of cardinals becomes a stunning mid-water feature.
Quick Specs
Water parameters
| Temperature: | 73–81°F (23–27°C). Keep it stable; warm water needs good oxygenation and consistent maintenance. |
| pH: | 5.0–7.0 (acidic to neutral; stability matters most). |
| Hardness: | 1–12 dGH (soft to moderately hard; softer is preferred). |
| Other: | Ammonia and nitrites must be 0 ppm at all times. Keep nitrates low (ideally under ~20 ppm) with regular water changes and controlled feeding. Cardinal tetras are sensitive to unstable or newly set up tanks, so a mature filter and stable parameters are key. Good oxygenation helps, especially at warmer temperatures. |
| Water changes: | Change about 25–35% weekly to keep water stable and nitrates low. In smaller tanks or heavier stocking, 15–25% twice weekly can improve stability. Consistency matters more than occasional large changes. |
Behavior & compatibility
Schooling Behavior: Cardinal tetras are schooling/shoaling fish and should be kept in groups. In a proper school they are calmer, more colorful, and show natural mid-water behavior.Temperament: Cardinal tetras are peaceful and not typical fin-nippers. Stress and poor conditions can cause skittish behavior, but they are excellent community fish when kept in a proper school.
Centrepiece: They are not a single centerpiece fish, but a large school can be a major visual highlight due to their bright red-and-blue stripe.
Prolific or Livebearing:They are egg layers (not livebearers). They may spawn in the right conditions, but they are not typically prolific in community tanks because eggs/fry are usually eaten unless separated.
Swimming zone:They are mid-water fish that spend most of their time schooling in the middle, rising toward the upper level during feeding.
Interaction with Plants:Excellent with plants and completely plant-safe. Planted tanks help them feel secure and display stronger coloration and more natural schooling behavior.
Setup essentials
Lid: A tank cover is preferred. They can jump when startled, and a cover helps maintain stable conditions and reduce evaporation.Filter: A filter is necessary. Use stable biological filtration with gentle-to-moderate flow. Clean water and consistent maintenance are especially important for cardinals.
Substrate: Dark sand or fine gravel is preferred, especially in planted or blackwater-style tanks. Dark substrate helps reduce stress and makes their colors stand out.
Lighting: Special lighting isn’t required, but moderate aquarium lighting is preferred for viewing and plant growth. Cardinals often look best with some shaded areas (floating plants or plants along the edges).
Heater: A heater is preferred and often necessary to maintain a stable tropical range (23–27°C), especially in cooler rooms or during seasonal swings.
Air Pump: An air pump is preferred if your tank runs warm, is heavily stocked, or has limited surface agitation. It’s not strictly required if filtration provides strong oxygen exchange, but extra aeration often improves comfort and reduces stress.
Feeding Regimen
Feed 1–2 times per day in small portions. Use quality flakes or micro pellets as staples, plus frozen/live foods (daphnia, brine shrimp, bloodworms) a few times per week for best color and condition. Avoid overfeeding to protect water quality.Lifespan
With proper care, cardinal tetras typically live about 4–8 years.Tank Mates
Good tank mates
peaceful community fish (harlequin rasboras, rummy-nose tetras, ember tetras), corydoras, otocinclus, bristlenose pleco (space dependent), peaceful gouramis, snails, many shrimp (adult shrimp usually fine).
Avoid
aggressive fish, fin-nippers (tiger barbs, serpae tetras in small groups), large predators, and very boisterous species that stress them.
Note
prioritize stable, clean water and a proper school size—cardinals are most impressive when kept as a large, confident group.
Common problems + quick fixes
Use a mature cycled tank, acclimate slowly, keep ammonia/nitrite at 0, and maintain stable temperature and parameters.
Increase school size (8–12+), add plants/shaded areas, reduce aggressive tankmates, and keep nitrates low.
Increase surface agitation, add an air stone, avoid overcrowding, and keep the tank clean.
Reduce feeding, improve filtration, and do consistent 25–35% weekly water changes (or smaller changes twice weekly).
Interesting Facts
Cardinal tetras often display their best color in slightly acidic, soft water with subdued lighting and dark substrate. A larger school looks dramatically better than a small group because their movement becomes more synchronized and they act more confidently. Their bright stripe can appear to “glow” under certain aquarium lighting, especially against dark backgrounds and plants.