Paige,
What tends to happen, is after several top off's (7-8) the cartridge filling tends to liquify (sp?) over, so although the cartridge looks full, because the fibers are no longer spread out like they were when the cartridge first started, the transfer from filling to the steel wool wick is hindered.
Does that make
sense? Liquid passes
through the fibers great when they are spread apart, and you can see each individual fiber. At top off and time goes on, you see the fibers starting to stick together and get all junked up. When this happens, liquid from the rest of the cart doesn't pass
through as easily and gets stuck.
I think I just tried explaining that twice...haha...hopefully one of the explanations you will understand.
That is why I tend to use 2 cartridges a day. After about 6-7 hours of use, I notice a lack in performance, and switch to a new cart. You can always try washing them however!