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How to properly read API test tube to color chart

  • Author evonner
  • Creation date
Many have asked how to properly interpret their test tube results with API Freshwater Master Test Kit. Many threads are out there with this question but comes with many different opinions. So, I contacted API for the "real" answer to this question. I believe that accurate test results are VERY important and that is why I am writing this article.

I started with a post to API's Facebook page via Messenger
: API Facebook Page

My Question: I/we need to know exactly how to read the correct color shade on the API liquid test solutions. If you hold the test tube directly on the on the white part of the color chart. It gives a darker color. But if you pull it away a bit so the light pierces the tube, you get a lighter color. Many of us in fish forums need the answer to this question. The packaged instructions are too vague.

API Response:

Hello Evonne, Thank you for inquiring at API. We would recommend to having a white background. The color is best interpreted when it is not touching the surface but holding away. We hope this helps!​

My Next Question​

How far should we hold it away?

API Fishcare​

There is no set amount of space. As long as it is not touching the surface.

I also sent a tech support message through API's website here is the response that I received by email: Towards the end of this email response has the contact information so if you have any questions, you can use this as a resource for all API products.

Hello Evonne,

Thank you for contacting API Technical Services.

The most important part of reading the result of the colorimetric tests is to match the hue of the test tube liquid to the most similar hue on the color chart, while avoiding shadowing of the test tube that could artificially cause the results to look darker.

Sometimes this shadowing can be avoided by using a good light source, that shines through the tube and onto the color chart directly.
In suboptimal lighting, the shadowing can also be avoided by pulling the test tube slightly away from the color chart, causing a gap that can minimize shadowing (or at least shift it to the side). There is not specific amount of space that removes the shadow – start at about a quarter inch and adjust as necessary.

As long as you are able to avoid reading the shadowed part of the test tube, you will have accurate results, regardless of which way you hold the tube.

We hope that we have helped! Please feel free to ask any follow up questions by replying to this email normally.

We also now offer an easy-to-use tool,
API® | AQUASPIN™ Advise ( designed to help you track what is happening in your aquarium or pond by providing customized recommendations based on your testing results, water appearance, and fish behavior. An unlimited amount of individual aquariums can be created on your free account and any retail store with an AQUASPIN testing machine can send results directly to AQUASPIN Advise for you.

Thank you,
API Consumer Services Team
Technical Services
T 1.800.847.0659
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