I have a feeling I'm about to answer my own question. Figure that might help sombody else in the future.
Have a 1997 hotsprings Sovereign.
Used t o have a 1990 or so prodigy.
Seems like there has been a sudden drop in ozone/bebbles comming out from the floor/drain/ heat inlet. If we assume the ozonator is all good, I bet its because i have a dirty filter. I like that on the newer ones the intake is via the filters.
On my old one the intake would clog with hair. etc. .Then the ozone bubbles would stop and evenyually the tub would overheat. The intake on that one was seperate frome filters and a real pain.

To answer myself.
cleaning the filter, though it wasnt particularly dirty, helped. I now understand my "injector" and that the filter not being clean was slowing down and straining the circulation pump. On this model the intake is through the filters.