Well, you can, but it's not a DIY thing.
Of course, you missed another alternative -- Disassemble the current tank and reassemble downstairs.
Jeff
That might be difficult, since I sold it last week. It was a 156.
This project springs forth from that. We moved about three months ago. I brewed up about 100 gallons of new salt water and had it in a new tub I had bought to put on line as sump in the dedicated fish room. It had been mixing/aerating and temp-regulating for about a week. When I brought the livestock over from the old place just a couple miles away, I put it straight into the new saltwater without acclimating. Big, big mistake. Although I can't be sure, I suspect that shocked the corals, they began sloughing mucous, each different species thought it was under attack and began sloughing defensively, and before you know it, you have toxic soup that took out all the corals (including some wonderful colonies that had come in on the live rock and prospered from nothing more than small patches), beautiful clams, beautiful RBTA's that had split three times on their own, and some amazing fish (eye-popping picasso perc's, pair of goldflakes, etc.). In the short time it took to go back to the old place, drain and disassemble the system, bring it to the new place, and move the tank down stairs, everything was dead. Unlike a sump overflow or fish going over the sides, etc., this was one of those event that you just turn off the light, tell your wife what happened (and show her a dead fish so she doesn't think you're pulling her leg like you usually do), and just go to bed since there's nothing you can do but accept it. Amazingly, though, my wife is the one who said don't sell off everything (as I'd done before when thinking I was getting out of the hobby), maybe sell the tank, and take the opportunity to set up the big system I've always fantasized about.
Had I known before moving the tank down stairs when we got to the house that the livestock was dead, it would have stayed up in the garage. Since everything died, however, it sat empty in the basement for three months, till last week. When we moved it back upstairs to sell it, however, I realized just how heavy and difficult it is to move "just" a 156. Sure, coming down the stairs would be significantly easier (even with the 45 degree bend to one side at the mid-flight landing), but still, a tank the size I want to do would be just too heavy to maneuver in the limited space available, even if I did it in acrylic instead of glass (preferred). It was with that realization that if I decided that if I want to have what I want, I am going to have to build it. (Seeing that they make and sell corner clamps at Home Depot is what gave me the courage to pursue this, since that alignment is, for me, crucial.)
This is clearly not going to be a back-and-forth-to-Home-Depot-while-I'm-doing-it type of project. This will be well planned, researched, and executed when thoroughly ready. As noted above, I will do a build thread when I start, but this is just planning phase, and one of the things that needs to be planned/researched is the silicone. Hence this post.