You can run that fountain with no filter in it. The filter only catches a few things -- a piece of kibble, a clump of hair. You will not notice much difference, plus you save $ not buying the darn things.

I never used the filters when I had the fountains. We also are always admonished to use charcoal filters in fish tanks. Again, it is just a way for the company to make $$ it is not necessary and experienced aquarists don't use them.