Fish Compatibility Checker
Check whether two species can safely share a tank.
How it works
Compatibility considers temperament, adult size, water parameters (temperature, pH, hardness), activity level and diet. Species are compatible when their parameter ranges overlap and neither will bully, eat or outcompete the other.
Advertisement
Formula & Method
Compatibility considers temperament, adult size, water parameters (temperature, pH, hardness), activity level and diet. Species are compatible when their parameter ranges overlap and neither will bully, eat or outcompete the other.
Example Calculation
Neon tetras + bettas: borderline. They share temperature/pH, but a nippy betta or a tetra nipping betta fins can fail. Neon tetras + corydoras: fully compatible.
Frequently Asked Questions
What makes two fish incompatible?
Mismatched water parameters, a large size difference that makes predation possible, aggression or fin-nipping, and very different feeding speeds. Size difference is the one people most often underestimate.
Can I keep any fish together if the tank is big enough?
Space solves aggression and territoriality but not predation or parameter mismatch. A large tank will not stop a big carnivore eating a small tetra, and it will not make soft-water fish thrive at pH 8.4.
What does a borderline compatibility result mean?
The pairing succeeds in some tanks and fails in others, depending on tank size, group numbers and individual temperament. Increase space and hiding places, keep proper group sizes, and have a way to separate them if it goes wrong.
Are bettas and neon tetras compatible?
Borderline. They share temperature and pH requirements, but a nippy betta will attack tetras and a nippy tetra will shred betta fins. It works in a well-planted 40-litre-plus tank with a calm betta, and fails otherwise.