"How do I know if my floor can support a large aquarium? Looking to put a glass aquarium (140# empty) on a wood stand (48"×48" footprint) in my 1st floor living room (over the basement). Aquarium would be placed against an exterior side wall. This side wall is poured concrete in the basement. The tank holds 93 g but some of this water will be displaced by rock and sand. There will be another smaller sump tank in the stand which holds an additional 20g. I estimate water at 100g/900#. I estimate the rock/sand weight to be 150#. Stand is 1/2" veneered plywood that is 48×48×48" with fairly bulky trim & shelf on the top but have no idea about its weight. I can send a picture if helpful ... Thank you for your thoughts! "
With the weights that you described you are pushing 80 pounds per square foot within the footprint of the stand. Most homes are rated for only 40 pounds per square foot of superimposed load. Looks like you will need some additional framing in the ceiling of the basement. Of course, posts are both the cheapest solution and the most intrusive solution (at least with respect to keeping the basement area open). If the ceiling of the basement is unfinished, you may be able to reinforce the joists upon which the aquarium rests with some engineered lumber beams. We can help you figure out the exact design but it certainly looks like you need to add some support beneath. Let us know if you need us to evaluate and provide a stamped retrofit plan.
By the way, yours is a pretty common question. I'm glad you asked BEFORE you installed the tank instead of AFTER, like some people!