Cardinal tetras are a popular freshwater aquarium fish prized for their striking coloration. Their shimmering bodies are mainly silvery blue with an iridescent red stripe running horizontally down the body. Their striking appearance makes them stand out in any home or office aquarium.
But how many of these colorful little fish can you keep in a 20 gallon tank? This is an important question for aquarists looking to start a cardinal tetra shoal in a standard 20 gallon aquarium.
Quick Answer
The general recommendation is:
- Minimum of 6 cardinal tetras for a 20 gallon aquarium
- Optimal number is 10-15 cardinal tetras for a 20 gallon tank
- Maximum you can add is around 20 cardinal tetras in a 20 gallon aquarium
So in summary, you can keep between 6-20 cardinal tetras in a 20 gallon tank. 10-15 is the ideal number for a 20 gallon to allow the fish to shoal properly.
Minimum Number of Cardinal Tetras for 20 Gallon
The bare minimum number of cardinal tetras you should keep in a 20 gallon tank is 6. This allows for proper schooling behavior, as these fish prefer to be kept in groups of 6 or more. Keeping just 1 or 2 cardinal tetras will cause stress and less display of natural behavior.
In a 20 gallon tank, 6 cardinal tetras meets the general rule of thumb for stocking small schooling fish: keep at least 6 individuals to allow natural shoaling behavior. With 6 cardinals, they will be comfortable enough to exhibit their natural schooling instincts by swimming together in an organized group.
Why 6 is the Minimum
There are a few reasons why most experts recommend keeping at least 6 cardinal tetras in a 20 gallon aquarium:
- Reduces aggression and nipping – Less likely to nip at each other in a larger group
- Natural shoaling behavior – Cardinals are social fish that prefer larger groups
- Security in numbers – Makes them feel more secure and less stressed
- Better display of social dynamics – Interesting to watch their social interactions
Going below 6 cardinals can cause stress, fighting, and abnormal behavior. So 6 is the magic minimum number for cardinal tetras in a 20 gallon tank.
Optimal Number of Cardinal Tetras for 20 Gallon
While the minimum is 6 cardinal tetras, the optimal or ideal number for a 20 gallon aquarium is 10-15.
Keeping 10-15 cardinal tetras allows them to exhibit their full range of natural schooling and shoaling behaviors. The larger group gives them security and reduces aggression or fin nipping.
In a 20 gallon tank size, 10-15 cardinal tetras makes for a healthy, active, and entertaining shoal. It also has the best visual impact, with their colors and schooling behavior on full display. This is the ideal cardinal tetra stocking level.
Benefits of 10-15 Cardinal Tetras
Here are some benefits of keeping 10-15 cardinals in a 20 gallon aquarium:
- Room for natural schooling behavior
- Reduced aggression/nipping
- More secure and less stressed
- Stunning when schooling together
- Ideal population density
- Prevents boredom/inactivity
The 10-15 range hits the sweet spot where water quality is maintained and the fish are comfortable and exhibiting natural behaviors.
Maximum Cardinal Tetras in a 20 Gallon
What is the maximum number of cardinal tetras you can add to a 20 gallon tank? Experts generally recommend:
The maximum cardinal tetras you can keep in a 20 gallon is around 20.
At around 20 cardinals, you are reaching the limit for a 20 gallon tank size. Water quality becomes an issue with larger numbers. Plus tank aggression and fighting increases due to overcrowding.
While 20 cardinals may technically fit in a 20 gallon aquarium, it is not ideal. The tank would be extremely overcrowded, with poor water conditions and increased fish stress. It is best to stay in the 10-15 range for a 20 gallon.
Dangers of Overstocking Cardinal Tetras
Some issues that can arise from keeping 20+ cardinal tetras in a 20 gallon tank include:
- Spikes in ammonia and nitrites
- Lower oxygen levels
- Aggression and fighting
- Stunted growth
- Stress
- Lower immunity – prone to disease
- Shorter lifespan
Overstocking leads to poor water quality, aggression, stress and disease. It is best to stick to 6-15 cardinals for a 20 gallon tank.
Other Stocking Considerations
When stocking cardinal tetras, you also need to factor in any other fish or creatures in the aquarium. Here are some other considerations:
Tankmates
If keeping cardinal tetras with other peaceful community fish like small rasboras, corydoras catfish, etc, then reduce the number of cardinals. For example, you may keep:
- 10 cardinal tetras
- 6 harlequin rasboras
- 6 corydoras catfish
The cardinals should be reduced to 10 to leave room for the other fish.
Aquarium Size
For larger tanks you can keep more cardinal tetras. For example, in a 30 gallon tank you can keep around 20-25 cardinal tetras. Reduce their numbers for smaller tank sizes.
Filtration
Good filtration allows for higher stocking levels. A 20 gallon tank with two strong filters can handle more cardinal tetras than one with a single weak filter.
Live Plants
Planted aquariums can support a higher bioload from more fish. The plants absorb waste and add oxygen. With lots of plants, a 20 gallon could handle closer to 20 cardinal tetras.
Summary
Here is a summary of how many cardinal tetras you can keep in a 20 gallon aquarium:
- Minimum: 6 cardinal tetras
- Optimal: 10-15 cardinal tetras
- Maximum: Around 20 cardinal tetras
To recap, the ideal number of cardinals for a 20 gallon tank is 10-15. This allows for proper schooling and the best water conditions.
Setting Up the 20 Gallon Aquarium
Here are some tips for setting up and maintaining a 20 gallon cardinal tetra tank:
Tank Dimensions
A standard 20 gallon aquarium tank has dimensions of 24″ x 12″ x 16″. This provides ample horizontal swimming space for a cardinal tetra shoal.
Aquascape Design
Create an aquascape with plenty of open swimming areas. Use driftwood, rocks and plants to break up lines of sight. Cardinal tetras like swimming through thickets of plants.
Substrate
Use a fine gravel or sand substrate. Avoid sharp substrates that could injure cardinal tetra bellies. A natural black substrate shows off their colors.
Filtration
Use an external canister filter or hang-on-back filter rated for at least 30 gallons. This provides enough filtration for up to 20 cardinal tetras. Install the filter properly to avoid water bypasses.
Heater
Cardinal tetras require warm water between 72°F and 82°F. Use an adjustable aquarium heater correctly sized for the tank.
Plants
Add several bushy stem plants like hygrophila and aquatic moss. Floating plants can provide shade. The plants absorb nitrates and provide territory markers.
Caves
Add caves and tunnels made from rocks or wood. This gives the cardinal tetras places to explore and feel secure.
Water Parameters
Maintain clean water with 0 ammonia, 0 nitrites and <20 ppm nitrates. Perform partial water changes of 25-30% weekly. Add aquatic plant fertilizer to feed the plants.
Tank Mates
Some suitable tank mates include: neon tetras, rummynose tetras, pencilfish, hatchetfish, dwarf cichlids, small catfish and shrimp.
Feeding Cardinal Tetras
Cardinal tetras should be fed a varied diet for good health and coloration:
- Quality flake foods or micropellets 1-2 times daily
- Live or frozen foods like brine shrimp or bloodworms 2-3 times a week
- Supplement their diet with spirulina powder or algae wafers for vegetation
Feed them in portions they can eat within a few minutes, 2-3 times per day. This prevents waste and water fouling. Take care not to overfeed.
Breeding Cardinal Tetras
While cardinal tetras rarely breed in home aquariums, here are some steps if you want to try:
- Condition the fish for 2-4 weeks by feeding frequent small meals of live foods
- Perform large (40-50%) water changes with slightly cooled, soft water
- Find a bonded pair that displays courting behavior
- Move the pair to a separate 10 gallon breeding tank with fine mesh plants
- Maintain warm water of 82-84°F and very soft, acidic conditions (pH 5.5-6.5)
- Dim the lights and provide subdued lighting
- Offer live foods like mosquito larvae and brine shrimp
- The female will scatter up to 100 eggs during spawning which the male fertilizes
- Parents should be removed after spawning or they may eat the eggs
- Fry hatch after 24-36 hours and are fed infusoria
It can be challenging but breeding cardinal tetras is possible if their specific conditions are met. The parents will likely need to be replaced each year.
Conclusion
To conclude, a 20 gallon aquarium can comfortably house between 6 and 20 cardinal tetras. The ideal number is 10-15 in order to allow them to properly school together and exhibit their natural behaviors.
When stocking your 20 gallon cardinal tetra tank, be sure to provide good filtration, regular water changes, an appropriate aquascape, hiding spots and a well-balanced diet. Maintain high water quality and these colorful little fish will thrive.
Cardinal tetras are excellent choices for small community aquariums. Their striking red and blue colors and active shoaling make them desirable fish sure to impress. By following the guidelines above on tank setup and ideal population density, you can enjoy a healthy and dynamic cardinal tetra aquarium.
