I used to love these replacement filters.  I knew when the water flow slowed that the filter needed replacing and I informed my cat sitters to watch for this.  With the new ridges on the updated filter design, this no longer happens.  I went on vacation and when I came home the fountain had milky water in it.  I have never seen this before but now I am sure it never happened previously because the water would have slowed to let me know that the filter needed changing. Now the water flows due to the gap which makes me wonder how useful the filter is if there is a path of least resistance.   The majority of the water will flow around the filter.  Please bring back the original design or I will need to change water fountains!