Finally, life is good...

[Aquattro]

Bob is right in as much as surface agitation is responsible for gas exchange. What Bob is wrong about is that all those bubbles that "don't matter", have surfaces, and that is where a large percentage of exchange takes place.
Deb et al., I am not sure why you continue to try and educate Bob. He has made it plain and clear for the last year that he is going to do things his way. I see no point trying to force a point like gas exchange. You do your thing, and Bob can exchange his gas anyway he sees fit. Please help the people that ask for help, for the are the ones that appreciate the effort. You all give really good advice, so give it to people that want it...