Main Power Problems... Circuit Breaker Trips Digital Air
Ozonator Troubleshooting,
Self-Contained/Portable Spa 
GFCI Breaker Trips 
By far, probably the easiest item (and most likely cause of GFCI tripping) known to troubleshoot.  Ozonators that are mounted on the floor, or the bottom of the spa equipment cabinet, and should immediately be suspect for tripping a GFCI.  Water invasion into the ozone chamber or into the ballast transformer will trip the breaker in milliseconds.
Example Installations
 
All Spa Installations

1.  First remove or turn off power at the remote disconnect box at the spa. 
2.  Disconnect the Ozone generator from the spa control.
3.  Re-Energize power.
4.  When the filter cycle starts, if the GFCI does not trip offline, then the ozonator is the culprit.

Dimension One Spa Owners:
Due to the design of the patented ozone system contained in your spa,  it is highly unlikely that your ozone generator will ever cause a ground fault.  However, it is always a good idea to eliminate it as a matter of practice.  (I have yet to see a single instance of a ground fault caused by an ozone generator in a D-1 spa in the last 3+ years).  If you have a GFCI problem in a D-1 spa, it's more than likely your circulation pump or heater element.