How can I prevent clogging of QIAfilter cartridges?
FAQ ID -1060

It is important to completely mix and lyse bacterial cells with plasmid Buffers P1 and P2. Incomplete mixing results in sticky or slimy areas of lysate, which will clog the filter matrix. It is recommended to completely resuspend cells in Buffer P1 and vigorously mix after addition of Buffer P2. Also mixing after Buffer P3 addition needs to be complete to allow fluffy precipitation of cell debris, which will float up. If the white debris does not float, dislodge it from the QIAfilter barrel wall (e.g. using a sterile pipette tip). Otherwise it will collect on the filter matrix and can lead to clogging. Use of LyseBlue reagent will help to achieve proper mixing results.