the purpose of your brace is obvious and as a result (if your tank is still filled) it now not giving the support it needs to; meaning your tank has probably flexed to some point. to make your repair you will want to relieve that pressure to allow the tank to return to its unfilled form. once you do this take a strip of clear acrylic (at least .25") and long enough to overlap the remaining portion of your original brace by a couple of inches. your goal here is to maximize your bonding surface area. when you pick up your strip of acrylic from a plastics shop (ask about some scrap, you might get it for free) and pruchase some weld-on #16. make sure your mating surfaces are clean (i use rubbing alcohol w/o any problem DO THIS ONLY ON YOUR NON-VIEWING AREA OF REPAIR). if you have any salt creep a little bronze wool should remove it. apply your weld-on to the repair area and apply some minimal pressure for about a minute, but not too much pressure. now, let set for 24 hours, then you should be able to refill the tank. BE VERY CAREFUL IF YOU DECIDE TO DRILL YOUR ACRYLIC! if you do not properly modify your bit, or purchase a specialized one you may crack your acrylic (you may not, but that is your choice). i hope everything works out for you.