If the base of the tank is a square, then the length and width are the same, making the area length*width*height=length*length*8=length^2*8=1268. Dividing both sides by 8, we get length^2=158.5 and by square rooting both sides we get length=sqrt(158.5)=around 12.6 for the length (and width), and 8 feet for the depth/height