Leave the tank on its classroom stand
The single best decision for a classroom goldfish tank is not to move it. Goldfish are hardy, but a car journey in a bucket, a strange room with different light and vibration, and then the whole trip in reverse a few weeks later is a far bigger shock than an empty classroom. The tank stays on its stand, the fish keep their familiar gravel, plants and hiding spots, and the filter's bacteria colony — the invisible workforce that keeps the water safe — never gets disturbed by a drained, sloshing tank. Everything else in the plan exists to support that one choice: a settled tank, lightly fed, in a quiet room.
Do the heavy preparation in the last school week
Work backwards from the final day of term. About a week before the break, clean the filter, but rinse the sponges or media in a bucket of water taken from the tank rather than under the tap, so the bacteria survive the wash. A day or two before the school closes, do one large water change, bigger than the usual weekly one, and test the water afterwards so you have a written baseline: if anything looks off mid-break, the caretaker can compare a fresh test against the numbers the tank started with. Resist the urge to do a last-minute deep clean of gravel and glass on the final afternoon — a sparkling tank with a knocked-back filter colony is a worse starting point than a slightly algae-flecked one with its biology intact.
Feeding and light run themselves — within limits
Goldfish and an automatic feeder get along well for a school-length break, provided the feeder is portioned and tested. Fill it, set it to drop a small ration once a day, and run it for several school days before the break while you are still there to watch: feeders are notorious for dumping double portions or nothing at all until they are dialled in. Slight underfeeding is the safe direction — goldfish produce a lot of waste, and uneaten food fouls water far faster than a modest diet harms the fish. Put the tank lights on a plug timer matching the school day's usual pattern, because weeks of darkness or a light left permanently on will stress the fish and grow an algae bloom respectively.
The empty building is part of the plan
A classroom in the holidays is not the same room: heating may be turned down or off, cleaners come and go, and nobody notices a tripped socket for days. Check with whoever manages the building what the heating does over the break, and move the tank away from a radiator or a sun-blasted window if the room's temperature will swing. Tape a note to the tank asking cleaners not to unplug anything or spray polish near the water, and ask for the sockets feeding the filter and feeder to be left strictly alone. A battery-powered air pump in the cupboard underneath is cheap insurance against a power cut quietly stopping the filter.
One named human still matters
Automation covers feeding and light, but it cannot spot a fish lying on its side. Name one caretaker — a staff member who lives nearby, the site manager, a trusted parent helper — who will look in roughly once a week, top up evaporation losses only with the pre-prepared container of treated water you leave beside the tank, and phone you if a fish looks wrong. Write their short routine down: look, count the fish, check the filter is humming, check the feeder still has food, leave. With the routine and the baseline test results shared through a KinsLe Care Pass, that caretaker holds everything they need for the visit without ringing you for details you are trying to holiday away from.