Can Cardinal Tetra and Figure 8 Puffer (Brackish) Live Together?
Cardinal Tetra and Figure 8 Puffer (Brackish) are not recommended as tank mates due to incompatible water types and 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
Behaviour & Temperament
Cardinal Tetra is a peaceful species (1/10), while Figure 8 Puffer (Brackish) is semi-aggressive (8/10). This notable difference means Figure 8 Puffer (Brackish) may occasionally assert dominance over Cardinal Tetra.
Large aggression gap (7 points) between Cardinal Tetra and Figure 8 Puffer (Brackish) increases stress risk for the more peaceful fish.
Cardinal Tetra and Figure 8 Puffer (Brackish) 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: Aggressive fish may bully and stress shy, slow-moving species. Hyperactive swimmers can stress shy, slow-moving species through constant motion. Shrimp eaters may also prey on very small nano fish.
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 Figure 8 Puffer (Brackish) (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 Figure 8 Puffer (Brackish) requires 10–25 dGH.
Crucially, these species require different water types — one needs freshwater while the other requires brackish conditions. This is a hard barrier to keeping them together.
Tank Setup
To house Cardinal Tetra and Figure 8 Puffer (Brackish) together, plan for an aquarium of at least 72 litres with a minimum length of 60 cm. This accounts for the larger species' space requirements with an additional 20 % buffer to reduce territorial tension.
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), Shells (Breeding/Hiding). 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.
Diet & Feeding
Feeding time deserves special attention with this pairing. Figure 8 Puffer (Brackish) is a known shrimp eater and may prey on small invertebrates or nano fish like Cardinal Tetra.
Frequently Asked Questions
Can Cardinal Tetra and Figure 8 Puffer (Brackish) live together?▾
No. This combination is not recommended. Key incompatibilities — such as different water type needs — make cohabitation unsafe.
What size tank do Cardinal Tetra and Figure 8 Puffer (Brackish) need?▾
A minimum of 72 litres (tank length at least 60 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 Figure 8 Puffer (Brackish) 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 Figure 8 Puffer (Brackish) aggressive?▾
Cardinal Tetra is peaceful (1/10) and Figure 8 Puffer (Brackish) is semi-aggressive (8/10). The gap in aggression levels means the calmer fish may experience stress from the more assertive one.
What pH do Cardinal Tetra and Figure 8 Puffer (Brackish) need?▾
Their pH requirements do not overlap. Cardinal Tetra prefers 4–7, while Figure 8 Puffer (Brackish) needs 7.5–8.5. This makes them incompatible in the same water chemistry.
Will Figure 8 Puffer (Brackish) nip Cardinal Tetra's fins?▾
Figure 8 Puffer (Brackish) is a known fin nipper. If Cardinal Tetra has long or flowing fins, there is a real risk of fin damage. Keeping Figure 8 Puffer (Brackish) in a larger group can help redirect nipping behaviour toward conspecifics.
How do I manage Figure 8 Puffer (Brackish)'s territorial behaviour?▾
Provide line-of-sight breaks using rocks, driftwood, and dense planting. A larger tank gives Figure 8 Puffer (Brackish) 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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