Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
Ineffective, no. Can easily be done with either a brute force or highly efficient setup. More costly over time and labor intensive than many prefer, yes.
Insufficient oxygen? Possibly. But can be blamed when it's not the case, since we have no way to measure O2 levels. Increasing flow and surface agitation may appear to solve the O2 problem, but as it drives off CO2 as well, which dissolved gas was really responsible?
In my experience, increasing CO2 from 30ppm (or less) to 60ppm in less than a day's time can severely stress fish that have not been acclimated to such high levels in the recent past. I suspect this is what you're seeing. If the increase is done over a week's time, the same fish in the same tank will happily tolerate even 80ppm.