Are you sure that harsh/bitter taste isn't because, because of the chain vaping, you're not allowing the wicking to catch up? Also, chain vaping, especially on a genesis, if you're not careful, can easily overcook the juice.
I chain vape, not 24/7, but plenty. Only time I run into bitter/harsh tastes is when the juice runs low on a dripper, the mesh wick doesn't have enough juice, or I overcooked the juice in the genny tank(though, thats less of a harsh taste and more of a funky/ruined juice taste)