The power connection shouldn't be flimsy, these problems can occur in three ways, the power connection on the controller has a broken solder joint to the board, the connector on the controller has a loose spring to contact the ground or the power supply has the wrong size tip (rare). I would open the controller, there are just two screws to open it and check that the two wires from the connector to the board are not broken loose, if that is OK, you will see the connector has a piece of spring steel that contacts the outer pole of the power connector and simply using a small screwdriver to bend it toward the center just a little will likely fix the problem.
The pumps are only $20 to replace, using kalk will shorten the pump life and does void the pump warranty, but usually it is OK so long as you plan to replace the pump after a year or so and make a dilute solution. I would also be careful that if you ever remove water for a water change the osmolator is unplugged and make the space between the float and optic sensor as close as possible so that you minimize the risk of an overdose shooting up the pH. If this is a new osmolator I would run it without kalk for a week or two to be sure everything is working properly.
