I've moved a tank with about two inches of sand in it, had no concerns. How deep is your sand bed? A calculator I just checked on says 200lbs should be around 6", if so that's about 1/4 of the total height of the glass, and I'd be a little worried with that much sand, but I think it could be done...
Instead of 50% water changes, consider dosing vinegar to reduce nitrates. Cheap and easy, works well, if you're interested there are many threads to be found on Google. Here's one:
http://reefkeeping.com/joomla/index....arine-aquarium