I also use the "starter" method, similar to how you keep sourdough going: leave a bit (of the previously-fermented feed) in the fermenting vessel each time to facilitate the next batch's ferment. And thicker is fine - the more soupy, the more active the ferment, but it will still ferment even if...
As @blackdog043 said, fermenting medicated chicken feed won't negatively impact the ferment. The reason is because Amprolium, the medication in the feed, works by preventing the coccidia protozoa from metabolizing thiamine (acting as a thiamine "antagonist"). Since Amprolium is not an...