I have been testing several proto type cells and never have had any foam produced at any time until I decided to use a soft set pipe thread sealer. I use this on the PVC cap screw lid. I had a drip from the thread and decided to seal this with the pipe dope. Only then did the foam start. This cell had run with out foam up till this point. So I new this was the only change and had to be the cause. I cleaned off all of the sealer and have had no more foam. When I disassembled the cell I found the sealer had become suspended in the solution and had crapped up the cell. I hope this may help prevent anyone else from having foam problems.