Freshwater fish compatibility checker for aquarium planning
Not every fish that fits in a tank belongs in that tank.
TanksConnected helps fishkeepers think about compatibility before problems start: size, temperament, territory, water needs and long-term stocking.
This public preview gives you a quick feel for the feature. Create a free account to save your own tanks, add livestock, record test results, and keep your aquarium history together inside TanksConnected.
Fish compatibility checker
Add fish, set quantities and tank volume, then run the same compatibility engine used by saved TanksConnected tanks. Results are guidance based on the species data available; individual fish behaviour can still vary.
Add fish to compare
Search by common or scientific name. For a proper check, compare adult fish, not tiny shop size.
The checker considers tank size, group requirements, stocking pressure, behaviour, territory, predation and overlapping water ranges using the current species records.
Compatibility result
Common fish compatibility questions
These quick checks help catch obvious problems before fish are already in the tank together.
- Can these fish live together?
- Will this fish eat smaller fish?
- Are Oscars and tetras compatible?
- Can aggressive and peaceful fish live together?
- What freshwater fish are compatible?
- How do I check fish compatibility before buying?
Extra compatibility guidance, FAQs and related tools
Size compatibility
Fish need to be judged by adult size, body shape and mouth size, not just how harmless they look in the shop.
Temperament compatibility
Peaceful, semi-aggressive and territorial fish need different stocking plans and escape space.
Water compatibility
Temperature, pH and hardness ranges should overlap enough for all fish to thrive long term.
Avoid the classic stocking headache
Compatibility mistakes are expensive and stressful. TanksConnected gives you a place to plan, review and adjust before the fish are already fighting.
Frequently asked questions
What makes freshwater fish compatible?
Freshwater fish compatibility depends on adult size, temperament, territory needs, water temperature, pH, hardness, group size and whether one fish could bully or eat another.
Can peaceful fish still be incompatible?
Yes. Peaceful fish can still be incompatible if they need different water conditions, different temperatures, very different tank sizes or if one species is small enough to be eaten.
Why does adult fish size matter for compatibility?
Adult size matters because many fish are sold small but grow much larger. A fish that seems safe in the shop may become territorial, predatory or too large for the tank later.
Should compatibility be checked before buying fish?
Yes. Checking compatibility before buying fish is far safer than trying to fix aggression, stress or water quality problems after the fish are already in the aquarium.
Is this a fish compatibility calculator?
Yes. TanksConnected can be used as a freshwater fish compatibility calculator or checker. Add the fish you are considering and compare factors such as adult size, temperament, water requirements and predation risk before adding them to the same aquarium.
How do I check aquarium fish compatibility?
Aquarium fish compatibility should be checked across several factors rather than one simple score. Compare adult size, temperament, territory, group size, temperature, pH, hardness and whether one species may bully or eat another.
What should I check for fish tank compatibility?
For fish tank compatibility, check whether every species suits the aquarium size and whether their adult size, behaviour, water requirements and social needs overlap safely. Fish can share similar water conditions and still be poor tank mates because of aggression or predation.