Thanks for the speedy reply! Interesting that you mention metal. I left it out of my original post, but the last water test said 0ppm copper and .31 ppm iron. The pool store considers the limit for irom to be .30, so they gave me a "metal out" product which I used. Our fill water source is our well, which is generally good (has been professionally tested for every contaminant known to man, as well as minerals and metals), but occasionally contains a little iron (seasonally depaning on groundwater levels and was <.03 ppm for Iron in January of 2012). Also, water gets to pool through hose on frost free hydrant which has some parts that could leach. My husband just added water (for the first time this year) today with that hose! Could the addition of new water w/ metals be reacting to earlier administration of "metal out" product? Maybe I should just let the pump go and see what we've got in 24hrs?

I will plan on getting the chlorine test you recommend and shock with bleach. Does it matter what bleach you use - obivously not the funny ones with added lavender scent, etc - but is there really any difference between the "splash-less" and all the other permutations out there these days and regular old bleach? I don't want to add anything that might cause any problem with the SWCG cell.

Thanks again.