The instructions say to view the test tube against the white portion of the card in good light.... but I'm finding that I can make the water match multiple colors depending on how close I hold the test tube to the white portion of the color chart card.
If I hold the tube right up against the card.. it matches the 40ppt color.
If I hold the tube just slightly away from the card, it matches 20ppt.
If I hold the tube about 2 inches away from the card, it matches 10ppt.
When I get a chance I think I'm going to go buy a different brand test kit... but I figured I would ask in case someone else here also found this and determined what the best 'distance from card' to read the API tests may be.
Edited by lowlevel, 29 March 2012 - 09:37 AM.