Like I said before, that's a big bio load to throw on a tank. You should do 10gal a week or so once you get this thing figured out. Are you using RO water? If not you need to be. How long was the 30gal up and running? I went up from a 75gal to 180gal and only used about 40gal out of the 75, the rest was fresh rodi salt water and I had no problems. If the 30gal was cycled, the sand bed was good, and everything else was good, I'm not sure what happened other than the extreme bioload where you went from none to a lot. I would feed maybe every other day until you get everything else under control, and just enough so they eat it. They're not going to starve. You'll have to test the water daily until you get it under control. Test tomorrow, and if it's not better do a 25% change and see. Are you running carbon, bioballs, or any other media, or a canister filter?
As far as a load bearing wall, I put mine next to the door where I exited the apartment. You can also use the wall between the kitchen and livingroom/hallway if you have one. Now that's what worked for me. At the time, Kelly Greens was rather new. There are some shady places in Spingfield now. But a 125 w/live rock shouldn't weigh over 1500pounds I wouldn't think.
