On a single-tank move, memory carries you. On a multi-tank move, memory is the first casualty: six near-identical bags in one box, two tanks with similar-looking tetras, a helper who helpfully puts the wrong bag in the wrong room. Labelling is not admin for its own sake — it is the system that replaces your memory at the exact moment stress, speed and wet hands make memory unreliable.
Give every tank a code before anything moves
Start a day early, while the tanks are still running and identifiable. Assign each a short code — T1 through however many you own — and write beside it, on a master list, the room it is going to and the stock it holds. Rename the tanks by code in your head from now on: not "the big tank" but "T3". Codes beat descriptions because they survive tiredness; two tanks can both be "the big one" at midnight, but there is only one T3.
The label that travels on the bag
As each fish is bagged, write directly on the bag in permanent marker — tape alone peels off wet plastic — the tank code large, then species, then the count: "T3 — harlequin rasbora — ×8". Add the warnings that change handling: a male betta or a territorial cichlid travelling alone gets "SOLO — do not combine"; a bag of fry gets "FRY — open first". Count out loud as fish go in, and write the count before the bag is tied, not after; recounting through plastic wastes the fish's calmest minutes in the bag.
Colour and count: the box system
Give each tank code a colour of tape as well, and band every bag and its box with it, so a glance sorts boxes without reading. Pack one tank per box wherever size allows, fish on the bottom layer, and write on the box's outside the code, colour, destination room and total bags inside: "T3 — BLUE — spare room — 5 bags". When a box is sealed, tick its line on the master list. At the new home, boxes go straight to their rooms unopened — distribution first, unpacking second, tank by tank.
Arrival: cross off, don't guess
Set up and fill the tanks in code order, and float each tank's bags in it before opening any. As bags are opened, reconcile against the bag label and the master list: eight rasboras written, eight rasboras out. Discrepancies surface now, while a missing fish is a search of one box, rather than next week when it becomes a mystery. Keep the list until every tank has been running a few days and every fish has been seen feeding — then the move is genuinely finished.
Labels work because they carry identity with the animal, which is the same principle behind a KinsLe Pet Pass: your pet's verified ID card keeps identity and your owner contact details easy to show anywhere — and the contact line your box labels carry means a box left behind anywhere can find its way back to you.