Says it takes both nitrate and nitrite to get ammonia level *shrug* The other tester i got was from seachem which was like 7 buck it says it last up to a year and you can buy for the actual testing you want done. That will be my next one to test out. I'm also thinking it would help when you go away stick in tank and when someone comes to feed your fish they just look at it and tell you the levels. Giving you an idea of how your tank is doing while your away. Or if something did happen you would know why it happened. Not everyone has the money to spend but if it will save you more in the end..... So worth it if it works.