I suspect it will crush down the carpet pretty well. However, most of the time you can steam the carpet back to near original condition. You may want to consider putting down a piece of plywood first...at least it would distribute the crush, rather than just the outline of the stand.
Also, and you probably already know this, but you may check with your land lord prior to setting up a tank of that size. Many leases exclude larger, or even any, fish tanks.
The plywood method will work great. especially if you attach small knobs or feet the wood. then you will only leave a small footprint in the carpet, not unlike any other furniture.
Thank you, I already have a 4ft near the kitchen on tiles and most things are ok as long as the place is the same as it was when we moved in and to my surprise the lease even says caged birds are ok.