I did a cleaning job on my 10 gallon ( do it 2 times a week) but today there were lots of bubbles from under the gravel... are these gas pocket? my tank water actually smelled like methane so Im assuming yes its gas pockets. its weird, I never have these, but also noticed them in my 29 last week. I always go thru the gravel to clean, whats up with these air bubbles?