Transport stress may reveal illness only after purchase. A separate quarantine aquarium protects the established community and lets you observe without adding shop water or pathogens to the main tank.
A complete simple setup
Provide species-appropriate volume, heating where needed, mature biological filtration, aeration, a cover and cleanable hiding places. Use separate labelled nets, hose, bucket and sponge, and work in the healthy aquarium before quarantine.
Do not use preventive antibiotics without a diagnosis
Watch appetite, breathing, swimming, skin, fins and faeces for several weeks while measuring water quality. Preventive or incorrect antibiotic use can select resistant bacteria in aquarium water; this risk has also been demonstrated in the ornamental-fish trade. Ask a fish-experienced vet to assess suspected bacterial disease and use antibiotics only under veterinary guidance. Antiparasitic and antifungal treatments are not antibiotics and require their own diagnosis and dosing. Extend observation after treatment.
