I have been very frustrated by the API test kit color determination (yes, I know, use Salifert... ! ... I'm going digital once my reagents are used up!), and last night was very frustrating. Not to mention that advice I got from this forum and others in-person said to hold the vial in contact and against the card.
API response to my online query says to hold it in front and off the card. See below screenshots.
API response to my online query says to hold it in front and off the card. See below screenshots.