I just installed a new pre-charged pressure tank.

The bladder went in the old tank.

Here is my problem: immediately after putting the new tank in, I noticed that the pump was cycling fairly often. I checked for leaks through the house and a hose bibs, and everything is fine.
I shut the pump off and the pressure gauge dropped from 40 psi to 0 over about 8 hours.

I can't figure out why. Even though the old tank's bladder was bad, when I charged it with a compressor, the water pressure held fine. Immediately after installing the new tank, I see the pressure drop off.

Doea anyone have any thoughts on what's possibly occuring or how to test further?

Thanks for any help.