Pond info: 50 gal stock tank, several plants, all healthy, water perimeters good per master test kit, 4 comets, 1 pleco, 1 snail. I treat all water before putting in the pond.

I am using an old-fashioned Lee's corner filter for aeration, mechanical and biofilter. It's simple and has done well. I rinse the quilt batting daily in pond water to get out the tons of algae and other gunk it filters out. I had charcoal and zeolite in the base of the filter and they were nicely colonized for a biofilter. I got some ceramic rings to replace the char/zeo upon recommendation. It has been in there for weeks, mixed with the char/zeo to colonize it, but it's not happening. The manufacturer said it would take 2 weeks to show the brown coating. Nothing.

Is there such a thing as bad biorings that won't work?