read the correct color!

  • #1
I know the API test kits are all the rage and are very accurate. My only concern since starting to use them is sometimes comparing your water in your test tube to the colors on the charts, especially if it's very close (like Nitrates 10ppm and 20ppm). I know the back of the card is white and should give you the correct color but I find lighting in the room effects it more than anything. I find it easier during daytime, with sunlight. At night I turn as much light on as possible and find the whitest room I can and read the results in there. However, what I found is that even a small tilt of the bottle changes the water color (or so it seems). I was retesting my nitrates earlier and luckily I could tell the color just by looking at the bottle (against a white wall), but then I placed it against the card. In one light, it read 5ppm, while tilting the bottle or moving it closer or further away from the color chart changed it anywhere up to 40ppm.

What are some tips to get the best readings? Or am I just dumb?
  • #2
I have the exact same problem. I was basically told that if it looks anywhere around 20 anyway just do water changes but for some reason I can't get mine below like 20 or 30 I just leave them I would just try and keep them as low as possible and then you don't have to worry about readings but I know it is very frustrating.
  • #3
Yup, I have the same problem, too. I sometimes ask my six year old son to verify the color match, figuring he's got younger fresher eyes, plus he is more decisive than me (I tend to over analyze). Anyway, for nitrates I always figure, I test the water once a week before and after the water change, and to be honest I don't really see the difference in color before and after. However, I figure as long as it looks like it is 20 or below it's good enough.
  • #4
I wouldn't count on sunlight as my standard light source for doing readings. It's not always available.

We use the hanging light fixture above the dining room table. The key here is that you're looking for consistency in your readings. That light source, for us, is consistent, whether it's day or night.

Hold the tube vertically against the white portion of the card, to the right of the colors choices. Tilt the card a little until you see one stripe of color running down the back of the test tube. This color will match, or be very close to, one of the color strips on the chart. This has proven to be a fail-safe method for us and there's no guesswork involved.
  • #5
When in doubt I hold the tube in front of the colored squares. The one that disappears should be the match.
  • #6
I was never sure if you were supposed to hold the tube over the white area of the card, or actually make contact between the two, but according to the Q&A with API, you are supposed to make contact. It usually raises the reading by a square (if that makes sense) doing it that way.
  • #7
Makes me wonder why they couldn't use better color choices like purple, blue, etc. Yellow and green are hard for people to see.
  • #8
they don't chose the colors for these, it is the reaction between the chemicals that produces the colors. I do a lot of these tests at work on a regular basis and most if not all of the certifiable tests use the same color standards.

As far as testing, I agree pick a light and always use that one. You will become actuate to your own tests and at lest have a stable environment for the fish.
  • #9
Good advise on the single strip of color and holding it against the paper... that was always unclear to me also.

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