Fish Compatibility Calculator
Compare two fish species to see if they can live together peacefully. Evaluate water type, temperament, temperature, pH, and tank size requirements for a harmonious aquarium.
How the fish compatibility calculator works
This tool compares two fish species across five key compatibility factors: water type (freshwater, saltwater, brackish), temperament (peaceful, semi-aggressive, aggressive), temperature range, pH range, and tank size requirements. Each factor is scored, and the overall compatibility percentage is calculated.
Select two fish species from the dropdowns below, then click Check Compatibility to see a detailed breakdown. The calculator highlights potential conflicts and provides recommendations for peaceful cohabitation.
Fish 1
Fish 1 Details
Select a species to see its details here.
Fish 2
Fish 2 Details
Select a species to see its details here.
Compatibility Results
Overall Compatibility
Side-by-Side Comparison
| Factor | Fish 1 | Fish 2 | Compatible? |
|---|---|---|---|
| Select two fish and click Check Compatibility | |||
Compatibility Breakdown
How Compatibility Is Calculated
Scoring System
Each factor is scored from 0 to 100:
- Water Type: 100 if identical, 50 if compatible (e.g., brackish with freshwater), 0 if incompatible.
- Temperament: 100 if both peaceful, 70 if peaceful with semi-aggressive, 40 if semi-aggressive with aggressive, 0 if aggressive with peaceful.
- Temperature: Based on overlap of temperature ranges (percentage of overlap).
- pH: Based on overlap of pH ranges (percentage of overlap).
- Tank Size: 100 if both fit the tank, 50 if one is marginal, 0 if too large.
The overall compatibility score is the average of all five factors.
Frequently Asked Questions
What is fish compatibility?
Fish compatibility refers to how well different fish species can coexist in the same aquarium. Factors include water parameters (temperature, pH, hardness), temperament, size, and dietary needs.
Can I keep freshwater and saltwater fish together?
No, freshwater and saltwater fish have completely different osmoregulatory needs and cannot survive in each other’s water conditions. They must be kept in separate aquariums.
What makes fish incompatible?
Fish can be incompatible due to aggressive temperament, different water parameter requirements (temperature, pH, hardness), size differences where one may eat the other, or territorial behaviour.
Can aggressive fish be kept with peaceful fish?
Generally no — aggressive fish will often bully, injure or kill peaceful tank mates. If you must keep them together, provide plenty of hiding spots and a large tank, but it’s not recommended.
What is the best way to introduce new fish to an aquarium?
Quarantine new fish for 2-4 weeks before adding them to your main tank. Acclimate them slowly by floating the bag and gradually adding tank water over 30-60 minutes. Always research compatibility first.
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