For people using Prime in their tanks: Prime acts as a binder for ammonia to make it safe. There are two types of ammonia in fish tanks. NH3 and NH4. One is free ammonia, and the other is ionized ammonia. Free ammonia is very dangerous to fish, the other is not as dangerous. The API Ammonia Test Kit only checks for the presence of ammonia, it can't tell you which it's detecting giving you a positive result when the only ammonia may be ionized ammonia. I'm sure that kit works well, but for those of us using prime, you want to use the Seachem MultiTest: Free & Total Ammonia test kit.Seachem MultiTest Ammonia Test Kit

The test works great, but the test tube is made of very thin glass and broke after just a couple tests. I was putting the cap on and the tube broke in half. I wasn't being rough either, just simply putting the cap on. Can't do much without that tube...