I am looking to replace the black round sponge filter for my K2R calcium reactor. I have tried the mail order vendors that sell the unit and the manufacturer, but they never p/u their phone. The LFS's sponges are not as porous as the orginal one.
Are you completely missing the sponge? Although you state LFS's sponges are not as porous as the orginal one maybe by chance look into the foam cell of a Rena filter that has 3 different densities. Cutting it to shape is how crafty of a DIY'r selfer. Hope that may offer an alternative.