I called Poolife support line and the guy explained to me they have two different NST products: one formulated for use in skimmers and one for in-line feeders. He said do NOT use the feeder product in a skimmer. The label on the feeder formulation (bucket with purple lid) is not crystal clear about this. Poolife guy acknowledged there is some confusion. My local pool store guy has only the feeder product in stock and he says he has used it in the skimmers on his own pool with no problem.