It says on the API test instructions that when you've shaken and allowed your sample to stand for 5 mins that you then hold it against the white background of the colour chart and match it to the appropriate colour to assess your parameters. I did a test this morning but before i held it against the colour chart i held it up to the front window and looked at the sample in natural light. It was a lovely shade of light orange (about 5ppm), which is pretty much what i expected after a large partial over the weekend. However, when i then put it against the white background of the colour chart the shade darkened, it was more like a deep orange/red (about 40ppm). Has anyone noticed the difference in shade between looking through the sample against natural light and placing the sample against the white background of the test chart? And more to the point, which shade do i believe?
