Not sure if that question is for @foxfish or myself @Costa
The main benefit of having the Co2 diffuser in front of the return pump is as the mist travels through the pump, up the pipe and out of the outflow more Co2 will dissolve into the water due to all the turbulent flow.
The remaining mist need not go all around the tank if the water is saturated to your desired ppm of Co2. A reactor dissolves all the Co2 by extending this turbulent period even longer.
So to answer your question, yes that additional flow and increased turnover from turning your return pumps up is gassing off Co2 to some degree. Whether you would want to do that is up to you and depends on several other factors.
The main benefit of having the Co2 diffuser in front of the return pump is as the mist travels through the pump, up the pipe and out of the outflow more Co2 will dissolve into the water due to all the turbulent flow.
The remaining mist need not go all around the tank if the water is saturated to your desired ppm of Co2. A reactor dissolves all the Co2 by extending this turbulent period even longer.
So to answer your question, yes that additional flow and increased turnover from turning your return pumps up is gassing off Co2 to some degree. Whether you would want to do that is up to you and depends on several other factors.