Can Cardinal Tetra and Red Fin Borleyi Live Together?
Cardinal Tetra and Red Fin Borleyi are not recommended as tank mates due to conflicting pH requirements and incompatible hardness ranges. Housing these species together is likely to result in stress, health problems, or direct harm to one or both fish.
At a Glance
Can your tank handle Cardinal Tetra and Red Fin Borleyi?
Compatibility is only part of the answer. Test both fish with your real tank size, current stock, and maintenance needs to see if you have enough space and a safe stocking level before you add them.
Behaviour & Temperament
Cardinal Tetra is a peaceful species (1/10), while Red Fin Borleyi is moderately assertive (6/10). This notable difference means Red Fin Borleyi may occasionally assert dominance over Cardinal Tetra.
Cardinal Tetra and Red Fin Borleyi both frequent the Middle (Open Water) region of the setup. This overlap can increase competition for space, so providing ample room and cover is important to keep both species comfortable.
Additional behavioural considerations to keep in mind: Hyperactive swimmers can stress shy, slow-moving species through constant motion.
Water Parameters
The safe temperature window for both species falls between 24°C and 28°C. Aim for the midpoint of this range (around 26.0°C) for optimal comfort.
The pH requirements of Cardinal Tetra (4–7) and Red Fin Borleyi (7.5–8.5) do not overlap, making it impossible to satisfy both species simultaneously.
Hardness requirements are incompatible: Cardinal Tetra needs 1–8 dGH while Red Fin Borleyi requires 10–25 dGH.
Tank Setup
To house Cardinal Tetra and Red Fin Borleyi together, plan for an aquarium of at least 280 litres with a minimum length of 120 cm. This recommendation combines the stricter species minimums with a community-load allowance so the pairing has realistic long-term space and filtration headroom.
Providing a mix of open swimming space and sheltered areas with rocks, driftwood, or plants will keep both species comfortable and allow natural behaviour.
Specific environmental needs for this combination include: Leaf Litter/Blackwater, Driftwood (Digestion/Hiding), Plants - Densely covered, Sand (Sifters). Meeting these requirements will help both species thrive.
Both species do well with low (still water) water movement, so a standard filtration setup rated for the tank volume should suffice.
Why This Pairing Usually Fails in Practice
Cardinal Tetra and Red Fin Borleyi are the kind of pair that can look acceptable in a shop but become a maintenance problem at home. The main risk is not a single number in the chart; it is the way incompatible behavior, water needs, or pressure on space compounds over time once both fish are established in the same tank.
Suitable Tank Sizes
Standard aquarium sizes large enough for both Cardinal Tetra and Red Fin Borleyi.
75 Gallon Standard
90 Gallon Standard
125 Gallon Standard
150 Gallon High
180 Gallon Standard
350 Liter (120cm Deep)
Show 1 more tank size
Frequently Asked Questions
Can Cardinal Tetra and Red Fin Borleyi live together?
No. This combination is not recommended. Key incompatibilities — such as critical behavioural conflicts — make cohabitation unsafe.
What size tank do Cardinal Tetra and Red Fin Borleyi need?
A minimum of 280 litres (tank length at least 120 cm) is recommended. This provides enough space for both species to establish their own areas and reduces the likelihood of territorial disputes.
What water temperature is best for Cardinal Tetra and Red Fin Borleyi together?
Keep the aquarium between 24°C and 28°C. A target of around 26.0°C sits comfortably within both species' preferred ranges.
Are Cardinal Tetra or Red Fin Borleyi aggressive?
Cardinal Tetra is peaceful (1/10) and Red Fin Borleyi is moderately assertive (6/10). The gap in aggression levels means the calmer fish may experience stress from the more assertive one.
What pH do Cardinal Tetra and Red Fin Borleyi need?
Their pH requirements do not overlap. Cardinal Tetra prefers 4–7, while Red Fin Borleyi needs 7.5–8.5. This makes them incompatible in the same water chemistry.
How do I manage Red Fin Borleyi's territorial behaviour?
Provide line-of-sight breaks using rocks, driftwood, and dense planting. A larger tank gives Red Fin Borleyi space to claim a territory without encroaching on the other fish's area. Adding décor that divides the tank into distinct zones works especially well.
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Guidarium Editorial Desk
Reviewed against Guidarium care, stocking, and compatibility standards. Read the editorial policy.
- Last reviewed
- May 3, 2026
- Last updated
- May 3, 2026
- Issues or corrections?
- Contact the editorial team
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