Tonight's test showed I lost 6ppm FC during the day (SWCG is off). It was partly cloudy today. I'll let the pump run overnight with the filter on to see how much I lose overnight.

If there is a loss, I think we can safely say something in the filter is consuming CL since last night with the pump off there was no loss. If the loss isn't that much I think I'll just let CL do it's job over time rather than tearing down the filter (or maybe shock it one more time). Tomorrow morning's test should tell us more.