Quote Originally Posted by chem geek
Possibly due to lower TA and higher pH that some people have. Maybe some SWG's produce different sized bubbles -- larger bubbles would be less efficient than smaller bubbles as was borne out by the "nozzle" experiment to lower TA.
I missed that, what was the nozzle experiment?

Quote Originally Posted by chem geek
Yes, using a cover significantly reduces CO2 outgassing. Or course, with an SWCG system, are people told never to use a cover or to only cover part of their pool? Otherwise they could build up a large bubble of hydrogen gas under their cover. It's not "explosive" the way propane would be, but it certainly burns (if ignited by flame or a spark) when mixed with oxygen (remember the Hindenburg!).
I have a cover and run the generator with it covered often. If it builds up a bubble, I don't see it. I suspect the cover is porous to hydrogen and it isn't getting a chance to build up. Your speculation does suggest an experiment though. Holding a lighter or match above the bubble stream of my primary return should produce some combustion if hydrogen is being produced. It would not be visible to the eye, but should show up on a digital camera or digital video camera. Those image sensors are quite sensitive to IR. Would chlorine burn too? Would there be a characterisitc color?

This is a don't try this at home, mythbuster kind of experiment. I suspect there is potential for real danger, small potential, but real.

Actually I am more tempted to look on the underside of the cover for discoloration. Since I see significant pH rises, if it is due to chlorine gas in the bubble stream going into my pool when the SWG is on, then there should be fading or hardening of the material above the first return jet where most of the bubbles enter the pool. Perhaps I can check those ideas out over the weekend.