FWIW I've never seen a black powder as a result, only grey / brown sticky paste.

My take is that since the zeolite is sort of acting like a catalyst and converting the CBD into another isomer (rather than actually reacting with it, as such ) and since Zeolite is pretty inert from a human consumption point of view, then an excess of zeolite isn't going to affect the results beyond diluting it a bit more.

In fact I have given up weighing my ingredients every time and just go with repeatable volumes:  one level, lightly compacted 2.5ml measuring spoon seems to be approx 1.75g of CBD , I then add a heaped 2.5ml spoon of zeolite to get something definitely active in the 30 mg range when consumed with chocolate.

I may be wrong about the above " a small excess is fairly harmless" theory though, and look forward to being corrected if necessary