After having built a lot of different cells I found my biggest enemy to be the Hydrogen leak. Unlike air or other gases Hydrogen is very light and will find the smallest hole to creep through! It will even crawl up through a small bolt thread if it can! What I'm getting at here is that if you look as though you are getting a good production but your bubbler says otherwise, start looking for leaks! The way I check is to connect up the cell and run it, then block the outlet with your thumb and spray water around all the suspect spots, yes, even the terminals! You will soon see a small bubble if there is a leak. Then its time to get the silicone sealer out! All the best.....keep it up!