I live in the projects luckily i don't pay for water and electricity, the best place to have a aquarium. I have a 150 gallon and so far doesn't seem to be collapsing. I wanted to upgrade for a while now but really afraid that one day I'll wake up with my tank missing and half my room torn down. I have it exactly at the windows I heard there were more stability and if it is more towards the outside of the building it would be stronger. By calculation my tank is roughly around 1350 lbs with 100lbs of sand and a wet and dry 30 gal filled about 1/4 so weighing around 60 lb with all the misc probably have 1600 pound in that one spot. Not counting me or my bed which is 8 feet away and my friends who.constantly sleep over. Any estimate of how much more I can hold? I want a 500 gal if possible or 300 bigger the better 
