I have a Red Sea Reactor 500 ( or something like that). It has the capacity to dissolve 180bpm. The directions say that the big bubbles being discharged are the other gasses in the chamber (like O2) that don't dissolve as quickly as the CO2 does. If you have a pressurized CO2 system, note that the CO2 in the bottle isn't pure (usually 95-99% pure depending on from where it came) so the big bubbles are probably the other gases in the bottle being expelled.
As far as the high/low, that depends on your bpm/bps (bubbles per minute/second)