So what you are saying is that you have several expensive tanks sitting outside you house where no one is guarding them and you have just let every reefing fanatic in and around ATL know, hmmm....
for the record, Just kidding!
Don't chance it.... a few years back I left my brew vessels ( 6 gallon and a couple 5 gallon galss carboys) outside during what I thought would be a heavy frost. Checked them later that morning everything looked fine.... later that week I went to pick one up and the the bottom fell out, literally. Lost 5 gallons and 2 of the 5 gallon. I know acrylic is different then glass, but why chance it.
Just heard... we are expecting snow on Wen up in my neck of the woods, oh boy!