Check compatibility between different tropical fish species and find their shared optimal temperature and pH ranges.
Stocking an aquarium is rarely a question of how many fish fit; it is a question of which species can share temperature, pH, hardness, aggression level, and minimum tank size without chronic stress. This calculator cross-references each chosen species against the others, returning the safe overlap of temperature and pH ranges, the recommended minimum tank size, and a categorical compatibility verdict (good, caution, or incompatible). It is built for community-tank planning where one wrong combination can wipe out months of stocking work.
Each species in the internal table carries temperature, pH, hardness, aggression, and minimum-tank-size attributes. When you add species to the calculator, the algorithm computes the intersection of those ranges. If any pair has no overlap (for example a cool-water white cloud at 18-22 degC with a discus at 28-30 degC), the result is flagged incompatible. Aggression mismatches (a peaceful tetra with a cichlid) and tank-size shortfalls also trigger warnings even when water parameters technically overlap.
Select two or more fish species to check if they can be safely kept together based on temperament, size, and water requirements.
If the result is 'Use Caution', you may need to provide plenty of hiding spots, use a larger tank, or monitor them closely.
Individual fish personalities vary. Always observe new additions carefully and be prepared to separate them if aggression occurs.
Compatible: species can be kept together in a typical community setup. Use Caution: works in larger tanks with hiding spots and careful monitoring. Incompatible: differences in temperament, size, or water requirements make cohabitation likely to fail.
Individual personality varies. Tank size, hiding spots, and group sizes all matter. Schooling fish kept in groups too small (under 6) often become stressed and nippy. Adding fish in the wrong order — territorial species first — also triggers aggression.
Most cichlids (especially African Rift Lake species) need cichlid-only tanks due to aggression and water chemistry needs. Some dwarf cichlids (rams, apistogramma) coexist with peaceful tetras and corydoras in soft, warm water. Check the matrix per species.
The ranges shown are the comfort zone for healthy long-term keeping. Brief deviations are usually tolerated. Long-term keeping outside the optimal range shortens lifespan and weakens the immune system, even if fish appear fine at first.
Apply the same principles: match adult size (no fish smaller than another's mouth), match temperament (peaceful with peaceful, semi-aggressive with semi-aggressive), and match water parameters (overlap in temperature and pH ranges). Research each species individually.