Permission first, in writing
Ask before the tank arrives, and get the answer in writing. A landlord weighing a request needs specifics, not enthusiasm: the tank's dimensions, its filled weight, where it will stand, and what sits under it to catch drips and spread the load. A large pleco setup is not a goldfish bowl — it is furniture-weight, plumbed-in equipment holding a serious volume of water above somebody else's floor. Written permission that names the tank protects you at inspection time and at deposit time, when an undocumented aquarium can otherwise be treated as an unauthorised alteration to the property.
Weight, floors and water damage
Work out the filled weight honestly: water, glass, substrate, rockwork and the stand together, then check the floor can carry it, ideally against an exterior wall where joists are strongest and the load sits over support. Keep the tank level on a proper stand, with a mat beneath, and place it away from the landlord's fitted flooring where a slow leak would do its worst damage quietly. Ask your insurer, and the landlord's, who pays if a seal fails — a cracked tank can release its whole volume in minutes, and renter's insurance that excludes aquariums is common enough to be worth one phone call before the tank is filled, not after.
A pleco outlives a tenancy
A common pleco can live for many years and grow far beyond the size it was bought at, so the rental question is really a succession question. How will the tank be drained, the fish caught and transported, and the glass moved when this tenancy ends? What if the next property has a no-aquariums clause, a top-floor room, or a landlord who simply refuses? Agree the fallback now — a friend with a suitable tank, a shop willing to take the fish, a larger permanent home already identified — while it is still a plan rather than an emergency. Responsible keeping of a long-lived fish in a short-term home is mostly this: never letting the fish's future depend on a decision you have not made yet.
Everyday practicalities in someone else's property
Build the tenancy around the tank from the start. Keep water-change hoses and buckets routed so spills are unlikely, and dry any splash immediately rather than letting it sit on flooring that is not yours. Give the landlord a sensible inspection routine — a quick look at seals, stand and floor each visit — and keep the area around the tank clear enough for that check to be easy. Note the condition of the floor and wall behind the tank, with photographs, on moving-in day, so normal wear near a large aquarium is never argued over later.
For household members who also follow the pleco, KinsLe's Family Sharing offers a way to share profile access with them directly.