Why a healthy-looking tank is not safe enough
A tank that held sick fish has shared its water — and whatever was in that water — with everything submerged in it. Bacteria, parasites, and their resting stages settle on plant leaves, in the grain of driftwood, and in the pores of rock and ornaments. Many survive for days or weeks on a damp surface, waiting for a new host. The saving grace is that very few survive being dried out completely: thorough cleaning followed by thorough drying is the home aquarist's most reliable disinfectant, and it costs nothing but time.
Sort by material before you start
Work through the pile by what things are made of, because the material decides the method. Smooth, hard items — glass, glazed ceramic, plastic ornaments, most stones — are the easy cases: they scrub clean and dry fast. Porous items are the risk: driftwood, lava rock, sponge, and unglazed clay hold moisture and microbes deep inside, dry slowly, and cannot be scrubbed below the surface. Live plants are a third category entirely, because anything harsh enough to guarantee disinfection will kill the plant along with the problem.
Hardy decor: scrub, heat, dry
Scrub hard decor under hot running water with a dedicated brush until every trace of algae and slime is gone — the biofilm itself is what shelters pathogens. Rinsing in a bucket of boiled water, poured over heatproof items, adds a margin. Then dry completely: not surface-dry, but days of drying in open air until even thick pieces feel bone dry all the way through. Sunlight and moving air help. Only then is the item ready to store or reuse.
Driftwood and porous pieces: patience or replacement
Driftwood from a tank with a stubborn or unexplained outbreak is the hardest call. Prolonged drying — weeks rather than days — makes it reasonably safe, and boiling smaller pieces is an option where size allows. But wood that housed a disease you never identified, or that still smells sour after drying, is wiser replaced: it costs little next to a stocked tank, and porous material gives you no way to verify it is clean. The same honesty applies to old filter sponge from the sick tank, which should simply be discarded.
Live plants: inspect, trim, quarantine
Plants cannot be scrubbed or dried, so handle them by inspection and isolation. Rinse them gently in clean water, strip off melting or damaged leaves and any visible hitchhikers you do not want, and then grow them on in a plain quarantine tank or bucket of clean, dechlorinated water with light for a couple of weeks. Time away from fish breaks the life cycle of many fish parasites, which cannot complete it without a host. Plants that deteriorate in quarantine were carrying too much damage to save and should be composted, not planted.
Rebuild with a record
When treated items go into the new setup, add fish gradually and watch the tank as you would any new stocking — the quarantine habits protect the new system while it proves itself. And note what was treated, how, and for how long: a simple list of the cleaning dates against each item on Care Teams on KinsLe stops anyone in the household returning a half-dried ornament to the tank because it looked ready.