Though this is a product endorsement, it does a nice job of explaining a little more about the ammonia(s) in the aquatic environment -- at least in a way that is fairly easy [for me] to comprehend. Whenever I'm learning something [about anything], I tend to only process the parts that I'm capable of understanding AT THAT PARTICULAR POINT IN TIME. I've read about NH3, NH4, and TAN [totals], but in my brain, it was all a jumble, so I would skip over the parts I wasn't ready to learn about yet. I'm glad I read it, 'cause I'm starting to understand the chemistry a little better [normally, I wouldn't even have looked at it]. http://www.koiphen.com/forums/showt...tance-of-Ammonia-monitoring-in-Mature-systems So, @Meyer Jordan, my API test kit says NH3/NH4 -- that means it's reading TAN [total ammonia]. So, does that mean that I have to calculate in the pH in order to know what's going on as far as how "toxic" the [NH3] ammonia reading is? See, it does start getting complicated...... GEESH! Or is there a way to know, other than by purchasing this Seneye product? Can you have a "0" TAN and still be having an "invisible" ammonia spike? Or does "0" mean "0"?