Every inflatable boat lives in its own environment and will experience varying conditions that will affect the tube’s pressure.  These conditions can include ambient temperature, sun, weather, water temperature, boat color, and so on.  Whatever the condition, inflatable boat pressure is affected since none of these can be humanly controlled.

This graph is an example of the daily high- and low-pressure variations that an inflatable boat experiences over time due to just the environmental conditions it is in.  Trying to optimize the pressure in a boat manually is nearly impossible.