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Store tanks mix species freely, and staff are busy. The result is a lot of tanks where one fish bullies the rest, eats its tankmates, or needs conditions the others cannot tolerate.
Key figures
- 76 to 81°F PetMD water temperature range for bettas
- 65 to 75°F PetMD water temperature range for goldfish
Four questions for every pairing
- Same temperature? PetMD gives 76 to 81°F for bettas and 65 to 75°F for goldfish. They do not belong together.
- Compatible size? A fish that grows large will eat small tankmates.
- Compatible temperament? Fin nippers and long-finned fish are a bad mix.
- Space for everyone’s needs? Schooling fish need a group; territorial fish need room.
Common mismatches
| Pairing | Why it fails |
|---|---|
| Goldfish with tropical fish | Different temperatures; goldfish outgrow them |
| Betta with fin-nipping fish | Long fins get shredded |
| Two male bettas | They fight |
| Small tetras with large cichlids | The tetras become food |
| A single schooling fish | Chronic stress without a group |
Building a calm community
- Pick one or two schooling species kept in proper groups.
- Add a bottom dweller suited to the tank, if space allows.
- Choose a centerpiece fish only if it is peaceful with the rest.
- Add fish gradually so the filter bacteria keep up.
Many popular fish are sold as juveniles. Look up the adult size of every species, and plan the tank for that, not for the fish you see in the store.
The stocking guide connects adult size and waste to the tank. The quarantine guide covers preparing for additions before fish share the community.
Questions people ask
Can goldfish live with tropical fish?
No. PetMD gives goldfish 65 to 75°F and bettas 76 to 81°F, and goldfish grow much larger and produce more waste.
Can a betta live with other fish?
Sometimes, with calm, non-nipping tankmates in a large enough tank. Never with another male betta.
Why do my fish keep dying after I add new ones?
Often too many fish at once, overwhelming the filter, or disease brought in without quarantine.
What are good fish for beginners?
Hardy, peaceful species that suit your tank size and temperature. Research each one's adult size and needs first.
Where these figures come from
- Betta Fish Care Sheet PetMD · petmd.com
- Goldfish Care Sheet PetMD · petmd.com
Figures last checked September 2026.
