How to Rebed a Mineral Tank – Step 3 – Add BlackCat® Cation Resin (Video transcript included below.) VIDEO TRANSCRIPT [EDITED]: Now that we’ve finished adding our underbedding–and in this case, that was garnet–we’re going to reset the scale and add the BlackCat® cation resin. Keep this resin in a sealed container. The reason you want to keep it in a …