Compatibility Overview
Molly and Rosy Barb can potentially coexist, but the combination requires careful attention. Some combination of water parameter differences, size mismatch, or temperament issues make this pair challenging. A larger tank (minimum 55 gallons), dense planting, and close monitoring are essential.
| Factor | Molly | Rosy Barb | Verdict |
|---|---|---|---|
| Temperature | 72–82°F | 72–82°F | ✅ 72–82°F |
| pH Range | 7.5–8.5 | 6.5–7.5 | ⚠️ 7.5–7.5 (narrow) |
| Temperament | peaceful | semi | ⚠️ Monitor |
| Adult Size | 4 in | 2.0 in | ⚠️ 2.0× difference |
| Min. Group | 3+ | 1+ | See below |
| Min. Tank Size | 55 gallons (for both species) | — | |
✅ Compatibility Positives
⚠️ Caution Points
Species Profiles
Molly — Poecilia sphenops
Hardy livebearers that prefer alkaline, hard water — sometimes slightly brackish. Prolific breeders; peaceful community fish.
Rosy Barb — Aquarium species
The Rosy Barb is a popular freshwater fish known for its vibrant coloration and peaceful nature. It is well-suited for community tanks with other non-aggressive species. They require a well-maintained environment and can be sensitive to water quality fluctuations. With proper care, they can thrive and add a splash of color to your aquarium.
Frequently Asked Questions
Can Molly live with Rosy Barb?
With significant caution and a larger tank. Molly and Rosy Barb can potentially coexist, but the combination requires careful attention. Some combination of water parameter differences, size mismatch, or temperament issues make this pair challenging. A larger tank (minimum 55 gallons), dense planting, and close monitoring are essential.
What tank size do I need for Molly and Rosy Barb together?
A minimum of 55 gallons is recommended for keeping Molly and Rosy Barb together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Molly and Rosy Barb?
72–82°F
Is a Molly aggressive toward a Rosy Barb?
Molly is peaceful and Rosy Barb is semi. Their preferred pH ranges are difficult to reconcile.
Related Compatibility Guides
Compatibility score breakdown
The overall score is weighted across water chemistry, behavior, adult size, swimming zone, and social needs. A score is a planning aid—not a guarantee for individual fish.
| Factor | Score |
|---|---|
| Temperature | 100/100 |
| Ph | 0/100 |
| Temperament | 75/100 |
| Adult Size | 72/100 |
| Swim Zone | 68/100 |
| Social Needs | 92/100 |
Tank size scenarios
Use the scenario that matches the actual group sizes and temperament you plan to keep.
| Scenario | Tank | When it applies |
|---|---|---|
| Minimum viable | 55 gal | Only for the recommended minimum groups, mature filtration, and close monitoring. |
| Recommended community | 75 gal | Adds territory, swimming room, and a safer buffer for behavior. |
| Low-conflict setup | 125 gal | Best when keeping larger schools or reducing territorial pressure. |