No, it's the Fluval Stratum!
It will pull kh for many months. How long it takes depends on how much you put in.
I prefer some kh in my tanks (I keep mine at 1 dKh) so I would just start adding enough baking soda at water change to get to whatever target you set. No more no less and preferably low so you don't see-saw back and forth. That's hard on shrimp. Eventually the substrate will "fill up" and then your additions will stick around.
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