The Slam info indicates that if FC level falls overnight it indicates contamination is consuming chlorine,and my test results at 10 PM showed FC at 6, but at 7 AM it down to 3. Am I just wasting time and chlorine?I believe the only source of contamination is the filter. I cleaned my filter cartridges a week ago, but I'm wondering if I they just have to be replaced. What are the recommendations for cleaning paper cartridges?