Can Black Fin Cory and Electric Blue Johannii Live Together?
Black Fin Cory and Electric Blue Johannii 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 Black Fin Cory and Electric Blue Johannii?
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
Black Fin Cory is a peaceful species (1/10), while Electric Blue Johannii is semi-aggressive (8/10). This notable difference means Electric Blue Johannii may occasionally assert dominance over Black Fin Cory.
Large aggression gap (7 points) between Black Fin Cory and Electric Blue Johannii increases stress risk for the more peaceful fish.
Black Fin Cory and Electric Blue Johannii both frequent the Bottom (Substrate) 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.
Water Parameters
The safe temperature window for both species falls between 24°C and 26°C. Aim for the midpoint of this range (around 25.0°C) for optimal comfort.
The pH requirements of Black Fin Cory (6–7.5) and Electric Blue Johannii (7.8–8.6) 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 Black Fin Cory and Electric Blue Johannii together, plan for an aquarium of at least 199 litres with a minimum length of 90 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), Smooth Gravel (Sensitive Barbels), Leaf Litter/Blackwater, Established Algae (Otocinclus). 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
Black Fin Cory and Electric Blue Johannii 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 Black Fin Cory and Electric Blue Johannii.
55 Gallon Standard
60 Gallon Breeder
75 Gallon Standard
90 Gallon Standard
125 Gallon Standard
150 Gallon High
Frequently Asked Questions
Can Black Fin Cory and Electric Blue Johannii live together?
No. This combination is not recommended. Key incompatibilities — such as critical behavioural conflicts — make cohabitation unsafe.
What size tank do Black Fin Cory and Electric Blue Johannii need?
A minimum of 199 litres (tank length at least 90 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 Black Fin Cory and Electric Blue Johannii together?
Keep the aquarium between 24°C and 26°C. A target of around 25.0°C sits comfortably within both species' preferred ranges.
Are Black Fin Cory or Electric Blue Johannii aggressive?
Black Fin Cory is peaceful (1/10) and Electric Blue Johannii 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 Black Fin Cory and Electric Blue Johannii need?
Their pH requirements do not overlap. Black Fin Cory prefers 6–7.5, while Electric Blue Johannii needs 7.8–8.6. This makes them incompatible in the same water chemistry.
How do I manage Electric Blue Johannii's territorial behaviour?
Provide line-of-sight breaks using rocks, driftwood, and dense planting. A larger tank gives Electric Blue Johannii 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 4, 2026
- Last updated
- May 4, 2026
- Issues or corrections?
- Contact the editorial team
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