Compatibility Overview
Molly and Threadfin Rainbowfish 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 | Threadfin Rainbowfish | 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.
Threadfin Rainbowfish — Aquarium species
The Threadfin Rainbowfish is a popular choice for freshwater aquariums due to its vibrant colors and peaceful nature. It requires a well-maintained tank with plenty of swimming space and a moderate water flow. These fish are not known to be aggressive and can be kept in community tanks with other peaceful species. Regular water changes and a balanced diet ar
Frequently Asked Questions
Can Molly live with Threadfin Rainbowfish?
With significant caution and a larger tank. Molly and Threadfin Rainbowfish 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 Threadfin Rainbowfish together?
A minimum of 55 gallons is recommended for keeping Molly and Threadfin Rainbowfish together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Molly and Threadfin Rainbowfish?
72–82°F
Is a Molly aggressive toward a Threadfin Rainbowfish?
Molly is peaceful and Threadfin Rainbowfish 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. |