Can Goldfish (Comet / Common) and Molly (Sailfin/Black/Dalmatian) Live Together?
Yes, Goldfish (Comet / Common) and Molly (Sailfin/Black/Dalmatian) are ideal tank mates. Both species share compatible water parameters and peaceful temperaments, making them well-suited for a community aquarium. A minimum tank size of 240 litres is recommended.
At a Glance
Behaviour & Temperament
Goldfish (Comet / Common) is a peaceful species (1/10), while Molly (Sailfin/Black/Dalmatian) is generally mild-mannered (3/10). This modest difference means Molly (Sailfin/Black/Dalmatian) may occasionally assert dominance over Goldfish (Comet / Common).
Goldfish (Comet / Common) and Molly (Sailfin/Black/Dalmatian) both frequent the Top (Surface) 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.
Water Parameters
The safe temperature window for both species falls between 24°C and 24°C. Aim for the midpoint of this range (around 24.0°C) for optimal comfort.
Both fish can tolerate a pH between 7.5 and 8. Maintaining a stable value within this band is more important than hitting an exact number.
For general hardness, the shared comfort zone is 12–20 dGH. Regular testing will ensure conditions stay within this range. An aquarium test kit is recommended for monitoring.
Tank Setup
To house Goldfish (Comet / Common) and Molly (Sailfin/Black/Dalmatian) together, plan for an aquarium of at least 240 litres with a minimum length of 120 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: Sand (Sifters), Smooth Gravel (Sensitive Barbels), Plants - Densely covered, Established Algae (Otocinclus). Meeting these requirements will help both species thrive.
Note a potential conflict in setup requirements: Goldfish (Comet / Common) is a plant destroyer, which conflicts with Molly (Sailfin/Black/Dalmatian)'s requirement for live plants. 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.
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Frequently Asked Questions
Can Goldfish (Comet / Common) and Molly (Sailfin/Black/Dalmatian) live together?▾
Yes. Goldfish (Comet / Common) and Molly (Sailfin/Black/Dalmatian) are considered ideal tank mates. Their water parameters, temperaments, and behaviour profiles are well matched for a community aquarium.
What size tank do Goldfish (Comet / Common) and Molly (Sailfin/Black/Dalmatian) need?▾
A minimum of 240 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 Goldfish (Comet / Common) and Molly (Sailfin/Black/Dalmatian) together?▾
Keep the aquarium between 24°C and 24°C. A target of around 24.0°C sits comfortably within both species' preferred ranges.
Are Goldfish (Comet / Common) or Molly (Sailfin/Black/Dalmatian) aggressive?▾
Goldfish (Comet / Common) is peaceful (1/10) and Molly (Sailfin/Black/Dalmatian) is generally mild-mannered (3/10). Their similar temperaments generally lead to a peaceful coexistence.
What pH do Goldfish (Comet / Common) and Molly (Sailfin/Black/Dalmatian) need?▾
Both species overlap in the 7.5–8 pH range. Consistency is key — avoid sudden swings, and test regularly to stay within this window.
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