I have alot of experience with a DIY CO2 generator, with similar setup to yours. My live plants were doing terrible, but once I started the CO2 going, they grew like they were on steroids !! Sounds like you're going fine. As the bubbles make their way to the surface, some of the CO2 is absorbed by the water, and the rest occurs when the CO2 bubbles pop at the surface. Some goes back into the air, some absorbed by the water. In a 55 gall tank, as long as you've got a decent stream of bubbles, this should be fine for any plants you put in their. You don't want to over do it and cause the fish to have CO2 poisoning either. The generator, I'm assuming you added dry yeast, sugar and water -- produces huge amounts of CO2 at first then it slowly changes to what is called anaerobic respiration inside the yeast chamber (the 2L bottle) and then CO2 production will come down -- but it's OK -- just keep it running and when the bubbles have almost stopped, time to make a new one. When I add tap water to the 2L bottle, I put alittle dechlorinator in it -- since the chlorine in the tap, can kill the live yeast and thereby decrease CO2 production. Have fun !!