Zeolite carries charges on its surface and acts as a non-specific absorbent of charged particles, including nitrate, phosphate and ammonium ions. Because it is non-specific, it will absorb everything else in the water column. Baked clay behaves exactly the same way and is used in kitty liter to absorb ammonium. If it were not for this activity, we could just use sand.
I'm not arguing over the technology, merely that there are other ways to achieving the objective.
Willie