The message is very simple. Do not buy API NO3 test kit. No. Do not do it. The reason is simple, let me explain.
The reason of buying a separated test was I do some experiments with liquid nitrogen so I need to measure results. I do not need a extremely accurate results, but a rough idea of the water in my fish tank could help. So I use NT Lab set of 8 different test, but because I use a lot of NO3 test, I started to run out of the test liquid. So I decided to but a big NO3 test. I chosen API.
First issue I found straight away is the chart. They printed the scale for 10/20 and then for 40/80 ppm using the same colour! How stupid it is!
Look at the picture:
Anyway, regardless the problem with the chart, I decided to do the water test straight away. Result was very scary. It told me that the water in my aquarium contains 160 mg/L of NO3. NT Lab test showed results of around 10ppm. Which one was lying then? I decided to do the tap water test. I know, my water supplier declares not more than 10ppm. In reality it means 10ppm of NO3 may happen, but usually it should be much less. I did tap water NO3 test and NT Lab showed what I expected: 0ppm, and result shown by the API Nitrate NO3 kit is… 40 or 80. No way.
One more time: DO NOT BUY API NO3 test. No. Do not. 🙂
Edit: 20.06.2020. Just to make the API test are really crap, and NT Lab test was OK, I decided to spend extra £15 and buy another NO3 test – this time I decided to buy JBL. It is actually a brilliant test with amazing idea of using a dummy test tube.
As a confirmation JBL and NT Lab test showed very similar result for a tap water: 5mg/L@JBL, 0mg/L@NT Lab.