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Shaking API tests

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I see widely varied results with many of the API tests depending on how much I shake each test solution.  I realize this has been discussed several times before, but the amount of variance makes me question the reliability of this information.  Additionally, while I originally selected the API test kit because of "cost effectiveness", if I'm spending inordinate amounts of time with each test, then perceived savings is gone as I'm burning through my own time.


Different results are obtained when I:

  • Shake the test solution 2-3 minutes, by hand
  • Shake the test solution 5-10 minutes, by hand
  • Shake the test solution 5-10+ minutes, by hand and beating it against hard surfaces

Because of this, I don't really know what the correct "shaking range" should be.........in theory results could be skewed by too much or too little shaking.  I'm considering purchasing a used vortex mixer because the idea of blowing this much time to have questionable results just doesn't sound like good science. http://lmgtfy.com/?q=vortex+mixer


Is this an inherent flaw of the API test kit, or can someone with experience give guidance on what they feel are the most accurate results/techniques?


I have a Pinpoint pH monitor but I've yet to break it out as I'm still in the process of getting my larger project set up.........I've also read all of the discussion regarding Hanna vs API GH testing.  I get the distinct feeling that expert level members use different diagnostic tools (aside from API), but thought it would be worth mentioning my experiences as well as getting a thread going so all could learn more about how to best use this specific brand of testing. 

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I have pretty much stopped using API. I do have many of their tests and can't afford to buy new tests for everything just yet. But I treat the results as having a very wide error margin.

What you say worries me, but does not really surprise me.

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are you talking about the api ph test or all of them in general? All of my api tests seem to give me pretty consistent results no matter how much shaking, expect my ph. My ph one does give me a lower reading the more I shake it around. I normally just do what the instructions say and I always get the same result that way. 

But I got tired of the color not matching anything on the chart obviously, so I ordered a ph pen.


Bottom line, I think they're cheap for a reason.



P.S. my ammonia test kit is never bright yellow either, even in my heavily planted tank that's been running a year. So yeah, refer to last line :P

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I'll admit that the GH test has less variance than the others, that said, I still have seen deviation when performing multiple tests consecutively from the same batches of test water.


I fully understand titrations (my background is in chemistry) and what variables may be involved that skew test results (specifically drop size from API test bottle), which is the reason that I've performed multiple tests in order to determine a mean.  From the Hanna vs API conversations, I understand that a "ballpark" GH is usually enough to get by.........I'm not as concerned about this test as much as pH or nitrate testing (both of which already have less-specific test results because of color interpretation).

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