Hi guys, went through a lot of discussion with Tom Barr on this topic offlist and he always mention that it only takes about an hour or so to return the CO2 levels back to the optimal range of 20-30ppm even after say 50-70% water change. I have tried different types of reactors (internals/externals), changing of flow patterns in the tank but have yet to get that type of fast response that he seems to be getting. Currently, my 20 gallon tank with a powerhead powered internal reactor takes about 3-5 hours to return the CO2 back to optimal range after a 50% water change. I would like to hear your views and personal experiences on this. Thanks in advance.