What is your Combined Chlorine (CC) reading? Also, if you have (or can get) an ammonia test kit from the pet/fish/aquarium store, what does it read? I don't think white water mold would generate that kind of chlorine demand, but if the FC level had dropped to zero and if your CYA level had dropped (did it drop from its level in the past?), then bacteria might have converted some or all of the CYA into ammonia and that can have a HUGE chlorine demand. If 50 ppm CYA got converted, for example, then that could require over 120 ppm FC to get rid of.
Do you have a Taylor K-2006 or TFTestkits TF-100 in order to measure such high FC levels? Or were you adding 10 ppm FC at a time or something like that?