You undoubtedly have at least what you call a "Slow Leak". Sometimes, they are slow enough that they don't bother you while you are riding but left over night or a a couple of days and the tire will be flat.

There is something causing this, so you should probably try putting it in water to find the telltale bubbles where it is leaking. Fill the tube with air, put it in a bucket and squeeze on the tube to find the bubbles if they are not apparent right away.

My hubby has been known to ride for miles on Slow Leak tires (he airs them up before he leaves each time). Me, I just find the leak and patch it or change to a new tube.

spoke