Good point, will check the borehole pump, as it is located in a field 500 metres away from the holding tanks to see if it is also running continiously.
It is difficult to see usage at the holding tanks as there are electrical trigger floats on the holding tanks that activate the borehole pump when they need replenishment.
Dont suppose you have the borehole pump electric metered? Those things can use A few KWh. If you do have a largish leak your electric consumption may have gone up a fair bit.