I agree. I don't know much about the Herbie other than what I have read the last couple of days, but by using this method instead of the vented Durso and maybe also positioning your overflow exit pipes in your sump under the water level in a manner to prevent as much agitation as possible wouldn't that come close to preventing significant Co2 loss? Someone please correct me if I'm not seeing something.
This sounds like the best possible senario, so that is what I am going to try. I am going change to a herbie method by bringing the return up over the back of the tank. Then utilize the small drain hole as the primary drain with a valve on it to create the full siphon. The larger drain hole will be the back up.
And then I will also eliminate the reverse durso in my sump and just exit the pipe under the water level. Might also go back to utilizing filter socks then as well.
I will update with the results. Not sure when I will get to this plumbing project.