Landlord does not have to know. But it would be good just in case any cracks or spills occur. I usto live in in a second floor in a house, and the floors were old and squeaky. Just a bit of Water fell and the landlord was ticked. I then moved out to a first floor apartment in a coop building with solid floors, no one below me. I then upgraded from a 55g to a 125g, it’s been 7 years with no issues. However the big issue is that I have to move next month or so and need assistance with the move lol. But overall, try to get you an apartment on the first floor in a building which is much better. If it’s in a house you must pray no one lives does stairs and if so, be very careful with spills and the RODI. Try to get the tank super leveled. Good luck