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Rainbows & Goldfish together?

Joined
Feb 18, 2026
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Location
India
Has anyone ever kept Dwarf Neon Rainbows (Melanotaenia praecox) with goldfish?

I have 4 fancy goldfish (either Fantails, Orandas, or some sort of hybrid of the two). They are around 4–5 inches each. I also have a school of 8 Dwarf Neon Rainbows in another tank (2 males, 6 females).

The rainbows are super sensitive to CO₂. The moment I cross around 30 ppm in my planted tank, I can see them struggling, so I’m thinking of shifting them to the goldfish tank, which has no CO₂.

The goldfish tank is 300 litres (4 × 2 × 2 ft / 80 gallons), and the rainbows are around 1.5–1.75 inches.

Usually people say no to goldfish tank mates, mainly because of a mismatch in temperature or temperament. But in this case:

  • The goldies cannot possibly eat the rainbows at their current size.
  • The rainbows don’t fin nip, or at least I’ve never seen them do it.
  • The water parameters in both tanks are quite similar.
  • Goldfish tank: GH 6, KH 2
  • Current rainbow tank: GH 4, KH 0
  • Temperature is pretty much the same in both tanks: 24–25°C (74–77°F).
Has anyone actually tried keeping Dwarf Neon Rainbows with fancy goldfish? Any issues I’m overlooking?
 

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