sorry, seems as though I was using a figure that included the tank weight, which threw off my division
saltwater weighs 9.2 pounds per gallon, but that can vary depending on the salinity, higher SG more weight
All Glass lists the filled weight of a 125 at 1400 pounds, I believe that includes the tank as well, not sure about the stand too, but lets assume it does.
then also let's figure at least 150 pounds of liverock and sand, probably much more than this.
let's figure the sump, which on a tank this big will probably be at LEAST 40 gallons, so add another 455 pounds per All Glass again
add perhaps another 50 pounds for equipment, livestock, etc...this may be too much but we did skimp on the rock weight.
total you are looking at around just over 2000 pounds
if you assume that the stand makes contact along the whole base then that weight is spread out over about 9 square foot which would mean about a little more than a 222 pounds per square foot, that is not a lot of live load, but a dead load like an aquarium, that is a LOT.
I estimate that my 55 with sump, rock, et all is about 800 to 900 pounds, spread out over 4 square feet of surface, but not really since only the edges of the stand touch the floor. figured out my tank puts about the same amount of weight per square foot onto my floor as your tank would. it is against a load bearing wall, in the smallest part of the room that barely fits it, so it has as much of the load bearing on the walls as possible...in addition I have decent floors, probably better than your floors sound like...I have some noticable deflection in the floor...
add the added weight of your tank and that is a LOT, unless the room you are keeping it in has no other furniture in it at all, the floor probably will not support this kind of weight for a long period
in a 10 by 20 foot room rated at 40psf you are utitilizing one fourth of the rated weight for the whole room in one small area, not wise
I am not saying the tank will crash through the floor, it may not, but it may even just tilt a little, causing seam stress and an eventual leak...a guy on the NORA board had a large tank, I believe around 100 or more gallons leak last year....MAJOR damage, I am talking thousands of dollars in damage, new floor etc.
my opinion don't risk it, save the tank until a better location, or trade it to someone for a smaller tank, like a 75 or something