I just hooked up an old BRS dual canister about two hours ago. Didn't see any decrease in airflow either. Got busy doing other stuff and just now thought to check the PH reading. It went from 7.6 to 8.1. I usually run between 7.7-8.0 throughout the day. Guess now I better keep an eye on my alk / cal consumption!No the lid is not air tight. In the pic you can see how I have it plumbed. I am running two canisters for the scrubber so when one media runs out I don’t see a drop in ph before I have a chance to change it.