That is the reason why I no longer use rock wool....I hate that shit. Give them a flush with a good flushing chemical like the one GH makes or Advanced then start back with just Ph adjusted water and some H2o2 for a few day's. Then change again this time with your regular nutrients. The flusher and H2o2 will help if there is any nutrient lock caused by your problem. Hydroponics recovers fast so you should be ok