Where to find a structural Engineer

[WarDog]

You say new house, does that mean just built, or new to you? New homes are much more over engineered than older ones.

If it's new, do you have access to the framing drawings from the builder? That would be a huge help.

Are you planning your tank in the middle of the room, on an interior wall, or an exterior wall? Different locations manage different weight loads accordingly.

Is the area below the tank unfinished? This would then be an easy structural modification.

A 300 gal tank including a safety factor will weigh approximately 4000 lbs. No typical floor is designed for this load.