Problem with new storage tank

I replaced my old well water storage tank which functioned just fine with a new bladder style tank and used all new fittings where it connects to the water line which supplies the house. When I turn on the breaker for the well pump the storage tank fills, then gradually loses pressure all the way down to zero on the pressure gauge. Today, i closed the gate valve at the tank and flipped off the breaker so the pump wouldn't run and I could hear air somewhere in or around the tank but if the tank itself was leaking or a fitting was leaking wouldn't I see water on the floor? I've read many comments indicating that this may be a check valve issue however that seems unlikely since the old tank held its pressure fine. If anyone has any advice please let me know. Thanks in advance.....

I assume the old tank wasn't a bladder style tank. How did the old tank get air? If it had a bleeder/snifter did you remove it from the line? If not, the bleeder might be bleeding off the pressure. If you removed the snifter with a checkvalve, it might have been the only holding checkvalve. The one on the pump or footvalve might be shot or there is a leak in the line.

The old tank actually was a bladder tank also with a shraeder valve. It was pretty old and I figured since I was remodeling the room Id go ahead and replace it. Hoping to eliminate problems down the road.

Tanks don’t “hold” pressure. Check valves “hold” pressure. Water can’t leak from the waters side to the airs side of the tank and make the pressure drop. Water has to be leaking out somewhere. If you can’t see it, then it is usually leaking back down the well. Either a bad check valve or a hole in the drop pipe.

OK thanks for the input. Ill look into replacing the check valve first and see if that solves the problem.