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Old 01-26-2022, 01:22 PM   #1
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API test kit inaccuracy

I switched from a Salifert test kit to a new API master test kit and I'm noticing that the nitrAte reading is higher than I think it should be. Has anyone else noticed this?

Here's the test I tried. I compared:
  1. tank water
  2. tap water
  3. bottled spring water
To answer some questions:
  • The kit has not expired.
  • I do the required shaking of bottle #2 and the final vial. The tank is a lightly planted 30 gallon well stocked with fish.
  • Tap water report showed no nitrAtes. (lab tested)
  • Assuming bottle water doesn't have nitrAtes.
The results
The spring and tap water did not look yellow. They were light orange and the tank water was a darker orange. So from this I am presuming that the test is off by 10 or 15 ppm.

Would anyone like to comment on this experiment and/or the results or share similar experiences?


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Old 01-26-2022, 03:05 PM   #2
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I would trust a water company report over your own test. So that would support your theory of an inaccurate test. However, water quality can vary over time and their test is just what it was when they did the test. I didnt used to have nitrate and now i do. Spring water is not purified so it could contain nitrate. Its unlikely, but possible. Did you do similar comparison tests with your old test kit?

In answer to your query, yes the API test will have a level of inaccuracy. So did your previous test kit. They are home test kits, not laboratory testing. Nitrate testing is especially tricky, even for professionals in a lab. So many things can throw off nitrate tests. If nothing else, telling 5 from 10 and 10 from 20 is very difficult and can vary depending on what light you look at it in.

My tap water report says nominal 7ppm nitrate, my own testing with API i would say 5 to 10 range. So from my experience its accurate enough. I think thats the thing to take from testing, its accurate enough for the purposes you are putting it too. Its probably correct that you have some nitrate in your tap and the spring water you tested, higher levels in your tank, but to expect it be an accurate measure is unrealistic.
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Old 01-27-2022, 08:58 AM   #3
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I did test my tap water with my original kit when I first purchased it but that was a long time ago. From memory, those results were closer to the lab reports for my tap water. So at the time I gave it a grade of "close enough".

I think the take away for me should be that the API tests are best used for following week to week or day to day trends within my fish tank.

Thank you again for taking the time to respond.

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Old 02-03-2022, 09:35 AM   #4
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That’s all anyone should be doing with these test results really. Like Aiken said, it’s a home test that literally costs Next to nothing per test, the accuracy isn’t going to be 100%.

Take the results for what they are and use them as a test by test comparison for yourself.
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