Curious about this: What about areas like mine that have a relatively high water table? My water is pretty perfect but in the winter is when the problem is the worst around here. People get flooding in crawl spaces and such, so the 10 ft deep end of my pool is certainly under the water table. Does this mean the valve is open a lot in the winter? If that groundwater with its cya-eating bacteria is getting in, that might explain the cya losses I have been experiencing every winter.