3 is not much of a problem, but if the system is working normally it should be 0 all the time. Probably time for a filter change or perhaps a membrane.
The style of setup you describe is really hard on membranes. You want to run your system for as long as possible. Rather than having the float switch turn the system back on every time you take any water out, it would be much better on the membrane to let the barrel get close to empty after several top offs, then turn the RODI
system back on and let it fill it back up.