Can Blue Back Blue Eye and Rachov's Killifish (Annual) Live Together?
Blue Back Blue Eye and Rachov's Killifish (Annual) are not recommended as tank mates due to incompatible water types. 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 Blue Back Blue Eye and Rachov's Killifish (Annual)?
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.
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Behaviour & Temperament
Blue Back Blue Eye is a peaceful species (2/10), while Rachov's Killifish (Annual) is generally mild-mannered (3/10). This modest difference means Rachov's Killifish (Annual) may occasionally assert dominance over Blue Back Blue Eye.
Blue Back Blue Eye and Rachov's Killifish (Annual) 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.
Worth noting: Blue Back Blue Eye is a known jumper, so a tight-fitting lid is essential.
Water Parameters
The safe temperature window for both species falls between 22°C and 26°C. Aim for the midpoint of this range (around 24.0°C) for optimal comfort.
Both fish can tolerate a pH between 7 and 7.5. Maintaining a stable value within this band is more important than hitting an exact number.
For general hardness, the shared comfort zone is 10–12 dGH. Regular testing will ensure conditions stay within this range.
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.
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Tank Setup
To house Blue Back Blue Eye and Rachov's Killifish (Annual) together, plan for an aquarium of at least 38 litres with a minimum length of 45 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: Driftwood (Digestion/Hiding), Sand (Sifters), Soil / Nutrient Rich, Leaf Litter/Blackwater, Plants - Densely covered. Meeting these requirements will help both species thrive.
Note a potential conflict in setup requirements: Blue Back Blue Eye requires Sand (Sifters), while Rachov's Killifish (Annual) requires Soil / Nutrient Rich. These substrate types may be difficult to provide simultaneously. Compromise where possible or prioritise the more critical need.
Both species do well with moderate (standard) water movement, so a standard filtration setup rated for the tank volume should suffice.
Suitable Tank Sizes
Standard aquarium sizes large enough for both Blue Back Blue Eye and Rachov's Killifish (Annual).
10 Gallon Standard
15 Gallon Standard
20 Gallon High
20 Gallon Long
29 Gallon Standard
30 Gallon Breeder
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Frequently Asked Questions
Can Blue Back Blue Eye and Rachov's Killifish (Annual) live together?
No. This combination is not recommended. Key incompatibilities — such as different water type needs — make cohabitation unsafe.
What size tank do Blue Back Blue Eye and Rachov's Killifish (Annual) need?
A minimum of 38 litres (tank length at least 45 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 Blue Back Blue Eye and Rachov's Killifish (Annual) together?
Keep the aquarium between 22°C and 26°C. A target of around 24.0°C sits comfortably within both species' preferred ranges.
Are Blue Back Blue Eye or Rachov's Killifish (Annual) aggressive?
Blue Back Blue Eye is peaceful (2/10) and Rachov's Killifish (Annual) is generally mild-mannered (3/10). Their similar temperaments generally lead to a peaceful coexistence.
What pH do Blue Back Blue Eye and Rachov's Killifish (Annual) need?
Both species overlap in the 7–7.5 pH range. Consistency is key — avoid sudden swings, and test regularly to stay within this window.
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