Instruct: Classify the given Amazon review into its appropriate rating category
Query: Slipping quality

I have been purchasing these for the last five years. The first three years these pool rx cartriges were excellent. I recommended them to several friends in my Rotary club. The last two years the quality and performance have gone down significantly. The last one I purchased was the poorest in performance. I suspect they have been made weaker so that you need to buy them more often. I will not purchase another one until they improve the quality. Jay Smith