It's my understanding that Clorine will disipate if water is left sitting for a while. Also that you can boil it out. I haven't heard that it during a freeze but if the movement of water as it sits, or is boiled removes it, I would think some or all would disipate when frozen. Strictly an opinion on a guess.

I think they have O2 generators now that work like pumps, similar to porterable generators used in the medical field.

You can also get non salt additives that are suppose to work as well as salt with those water O2 generators. I've never tried them, I do have some, but I don't know for sure if they work. Old dog new trick.. LOL