Can Molly live with Common Plecostomus?
These two species are usually compatible in community tanks.
Why Molly and Common Plecostomus Work
These two species overlap in both temperature (72–82°F overlap) and pH (7.0-7.8 overlap range). Their temperature tolerances are close enough, and neither fish pushes the pH so far outside the other's comfort zone that it creates chronic stress. The temperament match (peaceful + peaceful) is low-conflict. In a 55+ gallon tank with adequate hiding spots, these two can coexist with minimal problems.
Molly
Poecilia sphenops
| Adult Size: | 4.5" |
| Temperament: | peaceful |
| Min Tank: | 20 gal |
| Temperature: | 72-82°F |
| pH Range: | 7.0-8.0 |
Common Plecostomus
Hypostomus plecostomus
| Adult Size: | 15.0" |
| Temperament: | peaceful |
| Min Tank: | 55 gal |
| Temperature: | 72-86°F |
| pH Range: | 6.5-7.8 |
Water Parameter Overlap
| Parameter | Molly | Common Plecostomus | Overlap |
|---|---|---|---|
| Temperature | 72-82°F | 72-86°F | 10°F ✓ |
| pH | 7.0-8.0 | 6.5-7.8 | 0.8 ✓ |
Compatibility Breakdown
Temperament Match: peaceful + peaceful. Both peaceful → minimal conflict.
⚠️ Size Predation Risk: Molly (4.5") vs Common Plecostomus (15.0"). A 10.5" gap — the larger fish will view the smaller fish as food.
Score: 116.0/100 (GOOD ≥80, CAUTION ≥50, RISKY <50).
🔧 Tank Setup Requirements (for Both)
- Minimum tank: 55 gallons — sized for the larger fish in the pair.
- Temperature: keep it between 72°F and 82°F.
- pH: maintain 7.0 – 7.8.
- Hiding spots: essential for Molly — caves, plants, or driftwood to retreat when feeling stressed.
- Water changes: 25% weekly minimum. Two species mean double the bioload.
🔧 Tank Stocking Calculator
Enter tank size to calculate safe stocking levels:
Recommended Equipment
Based on tank size 55+ gallons:
Sinking wafers for plecos and bottom feeders
Explore Related Checks
See what else works with these fish:
Accuracy note: This tool uses expert rules + FishBase.org data. Individual fish behavior varies — a peaceful individual Molly may act differently from its species average. Always observe, quarantine new arrivals for 2-4 weeks, and avoid overcrowding. If a pairing says CAUTION, start with a smaller group and a lid.