I think part of it depends what's under the house. I have a 350 gallon system with powdercoated steel stand in my basement. I assume my tank with sump weighs well over 4,000 pounds concentrated in a single spot in my house. I talked to an architect and he indicated that depending how compact the clay is under the footings for the basement it's possible the weight could cause one part of the house to sink faster than the other side into the clay. That said, my house is brand new, I bought it new and had it built for me. So, there's a ton of settling for new houses. Something that's already settled and set in place will be fine. It's more with new construction the house spends a few years settling. I know that doors, windows, cabinet doors, all the frames are slightly off now. The builder told me this would happen that as things settle, doors would need to be adjusted, cabinet doors would too, etc. Garage door squeaks like crazy! Which is all from settling.
In short, do you need to worry? No... Do I? Maybe.