What could be the problem for the submersible pump, when it pressures up the bladder tank to cut off pressure of 50psi ,and then the pressure follow off to 30psi cut in pressure, only to drop the pressure in around 90 seconds, with nothing running in the house and no visible water leaks anywhere around the house or inside as well? Does the pump have a check valve on the bottom?:(

There is at least one check valve, sometimes more than one depending on the depth of the well. It does sound like that's your problem. You can put a checkvalve in above ground, between the pressure tank and wellhead.

Thanks, I've been researching on the web and have read about the valve. I'm going to install a check valve there between and reply as to my success. Thanks again!