Use a separate system
The quarantine tank should have mature filtration, suitable heat, cover and its own net, siphon and cleaning tools.
Observe normal function
Record appetite, breathing, swimming, skin, fins, body shape and waste. A fish that is merely surviving transport stress is not ready to breed.
Avoid shared water
Do not pour shop or transport water into the established aquarium. Prevent splashes and equipment sharing.
Do not medicate routinely
Quarantine is for observation and diagnosis, not automatic exposure to multiple drugs.
Reset carefully
After illness or mortality, clean and disinfect according to an appropriate protocol and allow the system to become safe and cycled again before reuse.