You first need to find the source. Test your tap water for ammonia. Also, does your municipal water authority (if on city water rather than private well) add chloramine? Chloramine is ammonia-related. You need t know where the ammonia is coming from, source water or tank.
Second, Prime is not a cure for ammonia for a few reasons. First, like any conditioner that will detoxify ammonia, it is intended to deal with initial ammonia such as what might occur in the source water at a water change, in order to give the bacteria/arachaea/plants time to deal with it going forward. If the ammonia is occurring from within the aquarium, these conditioners will not solve the problem and can actually make things worse.
Prime (and most other conditioners that deal with initial ammonia) detoxify ammonia by changing it into the basically harmless ammonium. But this change is not permanent; Seachem says it lasts 24-36 hours, after which the ammonium, if still present, reverts to ammonia. So that is what I mean by saying Prime and similar conditioners are not "cures" but temporary.
The other thing is that ammonia test kits like the API will test ammonia and ammonium as "ammonia," so a test for ammonia after using Prime will still show "ammonia" even though it is likely ammonium.
In acidic water, pH below 7.0, ammonia changes into ammonium so there is less of an issue. And plants and bacteria will take up ammonia/ammonium just the same.
EDIT. As I was typing, so was essjay...