As stated water is just over 8# per gallon (8.32# IIRC). Figure around 75# for rock and decorations (and that is just a ball park figure) and you are at 700#. Now add the equipment and light hood and anything else you can think of and you are going to want a stand that can hold 1000#, not to mention that you want to make sure your floor can suport that amount of weight in the foot print of the stand. I would not trust a file cabinet unless it is a fireproof cabinet that is built solid. You can build a cabinet or you can buy one. I know of people who have taken standard cabinets that they get ar garage sales for cheap and build up the inside with some 2x4's or 4x4's. The last thing you want it to put your tank, aka a lot of money, on a stand that will either fail or cause failure to your tank and then you have damaged equipment and a lot of water to clean up.