It depends on your diffusion efficiency in relation to your water parameters
. I say this because you might be like me and have extremely hard water and although you're diffusing the CO2 really well (high-pressure CO2, suitable reactor, low surface agitation, etc.), your pH and KH are naturally so high that you can't as easily keep the CO2 concentrations up (so you have to increase the CO2 flow rate).
Here's a link that has the same information as the page linked in a post above mine, however this page has fields that you can type your pH and KH values into and it will calculate the resulting CO2 concentration for you. This is good if one of those values is off the chart (as are mine).
Fightin' Texas Aggie Class of 2004
37 gallon AGA Black Seal, Emperor 400, Ebo Jager 200 W, 100% Flourite Substrate, 2x55 Watt AH Supply PC Lighting (5300K & 6400K) @ ~3.4 WPG, High-Pressure CO2.