how are you extracting it? I suggest you check the
Harmala Extraction Guide if you havent yet.
Im not sure of Sodium Hexacyanoferrate's reactivity or stability in acidic solutions, maybe some other chem expert can answer that. Though hexacyanoferrate's toxicity seems low, I dont know if its possible to generate some byproduct in the typical extraction environment. Personally I would avoid, the thought of cyanide gives me the creeps. Im sure you can find pure salt, just go to any natural food store or order it online, pure sea salt would work fine too.
And yeah, forget acetone. For cleaning up harmalas, repeat process of redissolving, filtering, and reprecipitating a few times.
good luck and keep us informed how its going