I'd recommend using the wood, to evenly spread the pressure, from the clamps, over the rim of tank... Slowly depress slightly, All the while Empting At Least a Trashcan worth of water before you do so... This should bring the distance between 2, even closer making it that much easier to tighten it... I'd use, More then recommended amount of clamps, for extra precaution, all the same style tho', so they all tighten at the same intervals as eachother... Should be able to get out a trashcan's worth without it allowing the corals to be out of the water, (BigTank), may be able to do more then a Trashcan, and can always move some corals lower for a temporary time if needed... New Tank, is ultimately the Best ideally... although Just welding metal together as a clamp, with a part to attach/screw the Acrylic Joist to run across, should work just fine, and don't have to worry about moving a sandbed and the others that goes along with a tank move.