P.S. to Chris:

Apparently there are quite a few users of this forum who live in areas where freezing is an issue and put antifreeze into their pipes. Clearly when they start up again in the spring, they flush this antifreeze into their pool water (at least for the return pipes from the pump/filter to the pool -- the drain/skimmer pipes could be flushed to waste, I suppose). I don't think anyone has had any problems with such antifreeze, but it is also probably true that they only use PG and not EG.