Sorry for the delay in getting back to you all, and thank you for all the different ideas
We set the tank on our table, and yup, it was still able to rock back and forth. So, we brought both back, and the guy at the store figured it must have been the stand. Set a different tank on the stand, no wiggling, no rocking/teeter tottering.
Put the tank we originally bought on the stand there, just to make sure that it wasn't our floor, and sure enough, it still rocked. Guy at the pet store had never seen a tank do that before. The original tank we bought had a massive bow towards the center, so all the weight would have been sitting there...I am so happy I was overly paranoid about this lol
So, I have my NEW new 75gal up on its stand! Waiting to fill it, still up in the air on whether or not I want to paint the back of the tank black...thinking I should make sure it holds water first
Again, thank you all for your help. I really appreciate it.
BTW, if anyone was curious of whats going in there, I have two Delhezi, one Teugelsi, and one Senegal (all around 3" long) waiting to move in there from their 20, along with a fancy goldfish...Goldfish came to me from my neighbor, she had put it in a one gallon bowl, with the water that it came from in the bag, and added warm water with no declorinater. Poor thing was near death when she, her son, and two of my kids told me if was floating upside down. I offered her my spare ten gallon, free of charge, she told me she didn't have room, and to just keep the fish.
I know long term, I am gonna have to find Coconut (goldfish) a home, luckily, he is HUGE compared to all the bichers I have, at least for now.