Tara,
I mix hardwood pellets in with wet coffee, if I have to use wet coffee.
Hardwood pellets are typically used for fuel, but they’re great for adjusting the for wet substrate. They’re processed into pellets (extruded) in a high heat environment and are completely dry so they’re very good at resisting any other contaminants, if they’re kept dry.
As well, the hardwood is typically completely natural and contains no chemical additives. Finally, they’re relatively cheap, at about $5 for 20kg (in Canada).