Review on 🐠 Ceramic Filter Rings for Aquarium Filtration - 140 Count - Compatible with C-Series and Magniflow Filters (PA11484) by Ashley Owens

So before washing I counted the number to know how much I had. The results are given in the boxes in the image. They are not very (if at all) porous. They are fairly smooth with a glassy surface. Even the fragments in the boxes are smooth except for the cracks. If it were a closed system I'd say take a hammer and smash to get the shards, but they should have been used in the contraption and the gravel itself. I'm trying to return them because I didn't receive the promised amount, they have big oil stains and I'm just afraid they will kill my snails and fish. I tried wiping the stain and the liquid that came out? from the rings and I cannot remove them without using a metal brush. It can dissolve in the tank and I'm concerned about contamination. If you absolutely must get them, which I don't recommend, rinse them out with water. The photo is difficult to see, but some have brown oily spots that are slightly raised.