Hi, I find that by the end of about 2 weeks, my 2 liter soda bottle still has plenty of fizz left if I shake it up occasionally, but will not fizz without the assist. Is there a better way to eke the last bubbles out before re-charging? Also, I was wondering if a corner filter with air stone, densely packed with floss, would work as a good CO2 reactor in a 20L tank? Thanks, Dinyar