hydrostatic force at the bottom of water tank

This is because the weight of the fluid is above it. The deeper the object is placed in the fluid, the more pressure it experiences.

If a fluid is within a container then the depth of an object placed in that fluid can be measured. Hydrostatic pressure is the pressure that is exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. Hydrostatic pressure increases in proportion to depth measured from the surface because of the increasing weight of fluid exerting downward force from above. For every 33 feet (10.06 meters) you go down, the pressure increases by 14.5 psi (1 bar). The deeper you go under the sea, the greater the pressure pushing on you will be. This is because of an increase in hydrostatic pressure which is the force per unit area exerted by a liquid on an object. You will start to feel an increase of pressure on your eardrums. But if you swim down into the ocean just a few feet and you will start to notice a change. We do not feel this pressure since the fluids in our body are pushing outward with the same force. The air around us at sea level presses down on us at 14.5 pounds per square inch (1 bar). What is Hydrostatic Pressure- Fluid Pressure and Depth

Hydrostatic force at the bottom of water tank