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Where are you finding the building up, is in below one of the jets, the filters, could it have come from the heater\pump?
If you had a small drip over time you would find a build up of chlorine as this would be left as the water evaporated, my guess is the water is leaking from the skimmer as if you have shock dosed the pool a lot would have gone done the skimmer.
If you can please upload a photo of what your seeing.