Start with weight and level ground
Before light, traffic, or looks, an aquarium's home is decided by what it weighs. Water is heavy, the glass, gravel, and rock add more, and a filled tank concentrates all of that weight on four small feet or one stand footprint. Place the stand on a solid, level floor, ideally against a load-bearing wall and across floor joists rather than along a single one, and never on ordinary furniture that was not built for the load. The surface must be truly level: a tank sitting even slightly tilted puts uneven stress on its seams, and a shim under one corner of the stand, not under the tank itself, is the fix. Decide this first, because once the tank is filled, it effectively does not move.
Keep sun, heat, and cold air off the glass
An aquarium wants the most boring temperature in the house. Direct sunlight through a window heats the water unevenly, drives algae across the glass, and can push a small tank's temperature up dangerously on a bright afternoon. Radiators, underfloor heating vents, and air-conditioning outlets do the same damage in the other seasons, cycling the water warm and cool as they switch on and off. Exterior doors and windows that open often bring draughts and cold spots. An interior wall in a room with a stable temperature is the classic answer: the water then changes slowly, and the heater does small, easy work instead of fighting the room all day.
Choose quiet over busy
Fish experience the room through vibration and shadow. A tank beside a television speaker, a games console setup, a piano, or a washing machine lives with constant tremors through the glass, and a tank in a hallway or beside the front door gets sudden looming shapes and door slams all day. Chronically startled fish hide, colour down, and stress. A living room corner where people sit still, or a bedroom or study, suits them far better than a playroom or corridor. The exception is the kitchen and bathroom point below: wherever you choose, people should pass it calmly and often, because frequently seen fish get their problems spotted early.
Plan for power and water changes
The best-looking spot fails if you cannot run the tank from it. You need enough sockets nearby for the filter, heater, light, and any air pump, with cables arranged in drip loops so water cannot track down a cord into the socket. You also need a route for water: buckets or a hose must travel between the tank and a sink or drain without crossing the whole house, and you need floor space beside the tank for a bucket during changes, plus headroom above the lid to lift it and reach in. Kitchens and bathrooms offer water but bring aerosols, cleaning sprays, and heat swings, so most keepers do better one room away with a bucket.
Put it where it will actually be watched
An aquarium thrives on attention, so the final test is human: put it where the household genuinely spends time, visible from a chair, not exiled to a spare room that is visited weekly. A watched tank gets fed measured amounts, its fish get counted, and a failing filter is heard the day it starts rattling. Once the spot is chosen, recording the tank's placement and its care routine in KinsLe Family Sharing means everyone in the house knows the setup is fixed and how the tank in that spot is looked after.