What is the weight of a 30 gallon fish tank full of water?

If the tank is actually filled to the brim (tanks never are) the water would weigh 8.35lbs x 30gallons which is 250.5 lbs. To obtain an accurate total weight you would have to add in the weight of the sand/gravel substrate, and the rocks (decore) and the weight of the empty tank. Then you would subtract the weight of the top 1 inch or so that is always left empty.