I talked to API about this issue, and they stressed following the instructions exactly, measure the time exactly according to the directions, etc. I have to admit - they are not exactly 'easy'Ive had api give me .5 to 1ppm ammonia when the real number is close to zero, i notice after 5 months it stops doing that for my tanks and appropriately reads 0, but its hard to say.
What I do know about API tests with my tanks is that it gets kind of sludgy, and I wouldn't rely on them. A few different batches of API ammonia have given me this issue, but I see others do not have this problem, so ymmv.

