Candidate
Guppy
Poecilia reticulata
A social hard-water livebearer with many domestic forms.
- Adult
- 3–6 cm
- Minimum
- 40 L · 45 cm
- Group
- 3
Condition-led guide · reviewed 2026-07-31
Peaceful aquarium fish for hard water
Species that can use mineral-rich water without forcing soft-water fish through chronic compromise.
Selection rules
What made the shortlist
- Test tap GH and pH after the water has stood and aerated.
- Choose within the profile range rather than chasing pH with chemicals.
- Plan livebearer reproduction and sex ratios before purchase.
Real photographed species
Options worth researching
Pick fish already suited to the source water, then compare temperature, activity and adult footprint.
Candidate
Endler's livebearer
Poecilia wingei
Small, active and strongly suited to mineral-rich water.
- Adult
- 2–4 cm
- Minimum
- 35 L · 45 cm
- Group
- 6
Candidate
Platy
Xiphophorus maculatus
A robust community livebearer when given its full group and footprint.
- Adult
- 4–7 cm
- Minimum
- 60 L · 60 cm
- Group
- 3
Candidate
Swordtail
Xiphophorus hellerii
A larger active option for long tanks with controlled sex ratios.
- Adult
- 10–14 cm
- Minimum
- 100 L · 90 cm
- Group
- 3
Candidate
Boesemani rainbowfish
Melanotaenia boesemani
A substantial shoal option for large, long hard-water aquariums.
- Adult
- 7–11 cm
- Minimum
- 200 L · 120 cm
- Group
- 8
Common mismatch
Fish to rule out for this brief
Hard water is not one number. GH, KH and pH describe different properties, and local reports do not replace a test.
Think again
Cardinal tetra
Paracheirodon axelrodi
Its reviewed range is centred on softer, more acidic water.
- Adult
- 4–5 cm
- Minimum
- 75 L · 75 cm
- Group
- 8
Think again
Chili rasbora
Boraras brigittae
Hard alkaline water sits outside its preferred range.
- Adult
- 1.5–2 cm
- Minimum
- 35 L · 45 cm
- Group
- 10
Think again
Discus
Symphysodon aequifasciatus
This specialist warm soft-water cichlid is not a fit.
- Adult
- 15–20 cm
- Minimum
- 300 L · 120 cm
- Group
- 6