I know this is a late entry but the question caught my eye and i thought i would share my experience. the short answer is YES - some conditions call for more than one ahh-some purge. in my situation I had a brand new spa delivered to my back patio, but my concrete pad was not yet ready -- so the wet-tested new spa sat in hot weather, growing biofilms. I could never get sanitizer demand down to normal levels because bad guys were lurking.
the long and the short of it is that a spa may require more than one purge. what i ended up doing is purging three times, and on the last time I put my cleaned filters back into their normal positions and ran an ahh-some treated spa just to prove there was nothing else to release. the cleaned filters actually released some small small amount of material which I wiped up with the micro fiber cloth, rinsing in a separate ahh-some solution. that did the trick for me - my CL demand went back down to normal and all was well after that.
My advice is that the spa is not purged properly until you are running an ahh-some treated spa and see no contaminant release. For severely contaminated spas this can take several purges.