Can Marlier's Julie and Red Tailed Black Shark Live Together?
Marlier's Julie and Red Tailed Black Shark 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 Marlier's Julie and Red Tailed Black Shark?
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
Marlier's Julie is a moderately assertive species (6/10), while Red Tailed Black Shark is semi-aggressive (7/10). This modest difference means Red Tailed Black Shark may occasionally assert dominance over Marlier's Julie.
Marlier's Julie and Red Tailed Black Shark both frequent the Bottom (Substrate) and 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: Two territorial species may clash over territory, especially in smaller tanks.
Worth noting: Red Tailed Black Shark is a known jumper, so a tight-fitting lid is essential.
Water Parameters
The safe temperature window for both species falls between 23°C and 27°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.
The pH requirements of Marlier's Julie (8.2–9.3) and Red Tailed Black Shark (6.5–7.5) do not overlap, making it impossible to satisfy both species simultaneously.
For general hardness, the shared comfort zone is 10–15 dGH. Regular testing will ensure conditions stay within this range.
Tank Setup
To house Marlier's Julie and Red Tailed Black Shark 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: Sand (Sifters), Driftwood (Digestion/Hiding), Plants - Densely covered, 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
Marlier's Julie and Red Tailed Black Shark 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 Marlier's Julie and Red Tailed Black Shark.
55 Gallon Standard
60 Gallon Breeder
75 Gallon Standard
90 Gallon Standard
125 Gallon Standard
150 Gallon High
Frequently Asked Questions
Can Marlier's Julie and Red Tailed Black Shark live together?
No. This combination is not recommended. Key incompatibilities — such as critical behavioural conflicts — make cohabitation unsafe.
What size tank do Marlier's Julie and Red Tailed Black Shark 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 Marlier's Julie and Red Tailed Black Shark together?
Keep the aquarium between 23°C and 27°C. A target of around 25.0°C sits comfortably within both species' preferred ranges.
Are Marlier's Julie or Red Tailed Black Shark aggressive?
Marlier's Julie is moderately assertive (6/10) and Red Tailed Black Shark is semi-aggressive (7/10). Their similar temperaments generally lead to a peaceful coexistence.
What pH do Marlier's Julie and Red Tailed Black Shark need?
Their pH requirements do not overlap. Marlier's Julie prefers 8.2–9.3, while Red Tailed Black Shark needs 6.5–7.5. This makes them incompatible in the same water chemistry.
How do I manage Marlier's Julie's territorial behaviour?
Provide line-of-sight breaks using rocks, driftwood, and dense planting. A larger tank gives Marlier's Julie 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.
Shared setup supplies
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Guidarium Editorial Desk
Reviewed against Guidarium care, stocking, and compatibility standards. Read the editorial policy.
- Last reviewed
- May 6, 2026
- Last updated
- May 6, 2026
- Issues or corrections?
- Contact the editorial team
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