Water and stored glycogen will only go away when it is depleted through exercise or carbohydrate restriction. This is not the same thing as storing fat. It is entirely possible to have full glycogen stores and still be metabolically well (i.e. normal insulin reaction and blood sugars).

The only way to know how much carb you can handle is to experiment. Don't make knee jerk asusmptions based on what happens after a day, or even a week or two. If you do not lose over several weeks on a higher carbohydrate allowance, that is probably your maintanence spot. If you gain slowly after several weeks, you are above maintanence.

If you gain a pound over night, this is not fat. This is water weight from glycogen. You are most likely not yet at your CCLM.