Tank Weight

[kakojones]

If the stand only has the four feet, I think you would still be fine. But I would prefer using a stand that has more contact with the floor to distribute more weight.

I still think a 75 should be fine. also...if you do and it falls through, I'm not a professional of any sort

 

[spiff]

Usually its easiest to just to look up from the floor below...
You won't see joists by pulling up the carpet...

 

[Greenaveli]

I wouldnt worry to much about a 75. If that fell through any floors I would gladly eat my hat.

 

[sweeTang21]

I would put the 2x4 under as well. Floor joist are set 16"oc and if you measure your stand your not going to be able to put all for legs directly over a joist. The wood will help distribute the weight across the whole floor.

either way i would worry much, the 1/2" T and G plywood they have been using for 50 years is some pretty sturdy stuff. Just the .02 of a carpenter