Submersibles can do a dynamite job IF you keep the vent tube free of humidity.
When humidity gets into the vent tube, the cool water surrounding the vent tube is generally below the dewpoint on muggy summer days. At temperatures lower than dewpoint, the humidity will condense out to water droplets, and the droplets will drain to the bottom of the vent tube.
The collected water at the bottom of the vent tube will exert a hydrostatic pressure on the 'low side' of the differential pressure sensor which should be vented to atmosphere and with no applied hydrostatic head on it. A hydrostatic pressure on the low side will produce an error where the level is reported as lower than the actual level, by whatever the height of the collected water is.
