Using standard testing, ammonia was at about 1.0 PPM - more than enough to kill fish and corals, and the tester never colored at all - it just stayed that happy sunshine yellow.
I put one on a tank at work and explained it,When I was away for a week all the fish died,and no one knew why,the spot was bright purple but no one noticed
my dog ate mine if you test your water regularly you should not need one! I think they arer garbage it lasted 1 week in my tank!! i was cleaning my tank and the dog got to it!!