If the tub is equipped with a whirlpool pump and an air blower, make sure each is connected to an independent GFCI circuit breaker.
Sometimes this breaker is very sensitive. Unplug the blower and plug in a hair dryer or light instead. If the ground leak detector (GFCI) trips again, a short circuit exists on the power line. Have the problem checked out by an electrician. If the problem still persists, the circuit breaker should be replaced.