well. for weight.. im perdy shure that the water is the heaviest of everything you will put in the tank.. ( water weigh about 8lbs a gallon.. and in 1 cubic foot area... you can hold about 7.5 gallons of water..) so the rock thing is nothing compared... imo... and as for a tank just exploding ... i had nover sen that personnaly but heav heard it happening when people set there tank and stand crooked ( not lvl) and uneven weight distribution causes the tank to explode..