A bubble of air of diameter 1mm sits attached to the bottom of cylinder filled with water.?

Question

Diameter of the bottom of the cylinder is d = 10cm, and
its height is H = 1m.
At some moment of time the bubble leaves from bottom
and floats to the top.

By how much the net force of pressure on the bottom
changed?

Cylinder is rigid and full of incompressible water
(except for the bubble).

Answer 1

When the bubble reaches the surface the water level decreases by bubble volume/surface area:
dH = 4/3 * pi * .05^3 cm^3 / (pi * 5^2 cm^2) = 0.00000667 cm
Pressure decreases by density * dH = 0.00000667 Pa.
I omitted any expansion of the bubble, since the net effect is the same as if someone removed the bubble from the bottom with a pipette. I trust you will run true to form and tell me why this is wrong.