Can Flag Tetra and Red Peacock (Ruby Red) Live Together?
Flag Tetra and Red Peacock (Ruby Red) are not recommended as tank mates due to conflicting pH requirements. 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 Flag Tetra and Red Peacock (Ruby Red)?
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
Flag Tetra is a peaceful species (1/10), while Red Peacock (Ruby Red) is moderately assertive (6/10). This notable difference means Red Peacock (Ruby Red) may occasionally assert dominance over Flag Tetra.
Flag Tetra and Red Peacock (Ruby Red) 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.
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 Flag Tetra (5.5–7.5) and Red Peacock (Ruby Red) (7.8–8.6) do not overlap, making it impossible to satisfy both species simultaneously.
For general hardness, the shared comfort zone is 10–12 dGH. Regular testing will ensure conditions stay within this range.
Tank Setup
To house Flag Tetra and Red Peacock (Ruby Red) together, plan for an aquarium of at least 208 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: Plants - Densely covered, Leaf Litter/Blackwater, Sand (Sifters), Smooth Gravel (Sensitive Barbels). Meeting these requirements will help both species thrive.
Both species do well with moderate (standard) water movement, so a standard filtration setup rated for the tank volume should suffice.
Why This Pairing Usually Fails in Practice
Flag Tetra and Red Peacock (Ruby Red) 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 Flag Tetra and Red Peacock (Ruby Red).
55 Gallon Standard
60 Gallon Breeder
75 Gallon Standard
90 Gallon Standard
125 Gallon Standard
150 Gallon High
Frequently Asked Questions
Can Flag Tetra and Red Peacock (Ruby Red) live together?
No. This combination is not recommended. Key incompatibilities — such as critical behavioural conflicts — make cohabitation unsafe.
What size tank do Flag Tetra and Red Peacock (Ruby Red) need?
A minimum of 208 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 Flag Tetra and Red Peacock (Ruby Red) 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 Flag Tetra or Red Peacock (Ruby Red) aggressive?
Flag Tetra is peaceful (1/10) and Red Peacock (Ruby Red) 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 Flag Tetra and Red Peacock (Ruby Red) need?
Their pH requirements do not overlap. Flag Tetra prefers 5.5–7.5, while Red Peacock (Ruby Red) needs 7.8–8.6. This makes them incompatible in the same water chemistry.
How do I manage Red Peacock (Ruby Red)'s territorial behaviour?
Provide line-of-sight breaks using rocks, driftwood, and dense planting. A larger tank gives Red Peacock (Ruby Red) 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 11, 2026
- Last updated
- May 11, 2026
- Issues or corrections?
- Contact the editorial team
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