apartments are made out of different materials depending on location, quality, age, and structural necessity. Please describe the apartment building in which these tanks may go in. as in how many stories, what kind of outside material, how does the floor feel when you jump inside it, high rise or just a 4 story tall building. Where you live. such as colder areas tend to use more concrete and temperate areas tend to use lots of wood. Any of that information would be able to tell us more about what the possible load the floor can take. Overall most floors are not designed to hold tons of weight so keep that in mind.
Also if the landlord cleared it, they probably believe that it can withstand the weight of the systems, but of course you might want to consult him again with that concern.