Anything wet that moves between tanks can carry trouble with it: a net, a siphon tube, a bucket, an algae scraper, even your hands. Water clinging to mesh holds far more than it appears to, and many fish pathogens survive comfortably in a damp net hung up overnight. While one tank holds a sick fish, treat every shared item as a bridge the illness could cross, and organise cleaning, order of work and storage so that bridge stays closed.
Dedicate First, Share Only If You Must
Start with the option that removes the problem altogether: a separate net, siphon and bucket reserved for the sick tank, marked with tape or a label that cannot be missed in a hurry. Sick-tank kit lives in its own spot, ideally in a tray or box beside that tank, never draped over a healthy tank's rim or dropped into the shared bucket by reflex. A second net costs little compared with treating a whole collection, and dedication removes the timing pressure that sharing creates.
Reserve the same thinking for smaller items people forget: thermometers moved between tanks, feeding tongs, plant tools and the jug used for water changes. If it got wet in the sick tank, it belongs to the sick tank until that tank is clear.
The Working Order for Every Session
Set the order once and keep it even when you are tired. Feed, test and maintain the healthy tanks first, with your everyday kit. Do the sick tank last of all, with its dedicated or about-to-be-cleaned equipment, and finish the session there. Wash and dry your hands thoroughly between tanks, and again after the sick tank, since hands are the piece of equipment owners most often forget to disinfect. If a healthy tank urgently needs the net after the sick tank has used it, that is exactly the situation the cleaning sequence below exists for; never shortcut it because the fish look fine.
Cleaning, Disinfecting, Rinsing and Drying
Work through the sequence in full, in this order. First, scrub the item under running water to remove algae, mucus and debris, since disinfectant works poorly through grime. Second, disinfect it using a fish-safe method suitable for aquarium equipment, following that method's own instructions for contact time. Third, rinse exhaustively under clean running water, far longer than feels necessary, so no residue can ride into the next tank. Fourth, dry the item completely in the air, ideally in sunlight on a clean surface, and do not return it to service damp: thorough drying alone defeats many fish pathogens, and it is the step that finishes the job the disinfectant started.
Buckets and siphon tubes need the same four steps inside and out, and nets should hang open rather than balled up, so every fold of mesh actually dries.
Storage That Keeps the Separation Real
Store cleaned healthy-tank equipment dry, off the floor, in its usual place. Store sick-tank equipment separately and still labelled, even after cleaning, until the sick fish has recovered and the tank has been clear for a sensible spell agreed with whoever is advising you. If the sick fish dies or the tank is stripped down, clean and dry everything thoroughly before any of it rejoins general service, and consider retiring a porous or cracked item that cannot be cleaned properly. Damp storage undoes good cleaning, so a dry, ventilated shelf beats a sealed wet box every time.
Pin the routine inside the cupboard door for anyone feeding the fish, and record each cleaning in KinsLe, where the Pet Passport files the log beside every tank's health notes.