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I doubt that a concrete pad would be a deal breaker for a home sale. If you leave your hot tub, with the pad, I would see it as a perk for the buyer (it certainly was for me when we bought our home). If you take your tub with you, you can sell the pad to prospective buyers as a nice place to put a gazebo or picnic table, etc.... -Just my two cents.
To add to the discussion, I was just told that I have a floating pad in the back. Something similar to this:http://midcenturymonster.files.wordpress.com/2011/03/16-back-patio-under-deck.jpgHe's saying its a floating pad and the tub can tilt because of the immense pressure a spa will put on it. Is that true?