There is some misunderstanding here concerning Prime, I'll come back to that.
First, to @blairsmith do they add chloramine to your water? And do you have live plants in this tank, and if yes, which plants (a photo would answer this best)? I will offer more when I know these things.
As for the Prime, it temporarily detoxifies ammonia by changing it to harmless ammonium. Most test kits like the API will detect ammonia/ammonium the same, as "ammonia." Nothing wrong in this, provided the ammonium is dealt with within 24-36 hours, by plants or nitrifying bacteria. If the (now) ammonium remains after 36 or so hours, it converts back into ammonia. However, in acidic water (pH below 7) "ammonia" is basically "ammonium" permanently so that is no issue. If the pH in the tank is above 7 the ammonia is more toxic.
First, to @blairsmith do they add chloramine to your water? And do you have live plants in this tank, and if yes, which plants (a photo would answer this best)? I will offer more when I know these things.
As for the Prime, it temporarily detoxifies ammonia by changing it to harmless ammonium. Most test kits like the API will detect ammonia/ammonium the same, as "ammonia." Nothing wrong in this, provided the ammonium is dealt with within 24-36 hours, by plants or nitrifying bacteria. If the (now) ammonium remains after 36 or so hours, it converts back into ammonia. However, in acidic water (pH below 7) "ammonia" is basically "ammonium" permanently so that is no issue. If the pH in the tank is above 7 the ammonia is more toxic.