The concentration of prazi in GC is slightly lower than Prazipro. So for whatever reason the liquid version poses a much higher risk for issues in QT when mixed with copper. Used solely there is no issue and I prefer prazipro over GC.
Bacterial bloom from the Prazipro is a result of the oxybispropanol it is dissolved in. Oxybispropanol is an alcohol, so it is essentially like you are carbon dosing (ie vodka/vinegar dosing)