Currently setting up a new tank but it's been a while since I've done a fishless cycle. I normally use Seachem Prime as my tap water conditioner but after reading the instructions I'd forgot that it also removes Ammonia. Is it best to avoid using Prime before starting the fishless cycle with household Ammonia? I have a bottle of API Stress Coat water conditioner that I could use. That only removes chlorine, chloramines and heavy metals.
No, it's fine to use Prime. It doesn't remove ammonia, it just converts it to the form less toxic to fish (NH4+). NH4+ remains available to filter bacteria and is just as useful to them as the more toxic NH3 so the cycle will proceed in exactly the same manner. Additionally, as the API ammonia test works by using the first reagent to force all ammonia to become NH3 and the second then measures it, your test results during cycling will be absolutely as normal too.