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Do you have an above ground pump or is the pump in the well?
Then you could have worn pump parts or a leak in the suction line.
Tank has nothing to do with this issue
Sounds more like an issue with the pump than a leak in the suction line if pressure doesn't drop (@ 18-28 psi) with nothing running.
You could try repairing the pump or replace it.
Yes low water level in the well is a possibility but not very likely if the pump holds 18-28 psi and shuts off at 28.
Do you have more questions?