I always laugh at people who say API test kits aren't as good as others. And I know lots of people will disagree with what I say here.
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I use API and I have used Salifert and Red Sea as back ups for a long time. In my personal experience I've found API to be just as reliable as the others. I'll do a test with an API kit and if I get a result I think is off (I've been doing this for 15 years now, I know a bad result when I see one) I test again. If the bad result is replicated, I'll pull out the Salifert or Red Sea test kit and run another test. And more than 99 times out of a hundred, the Salifert or Red Sea will give me the same result as the API. I only set up this 'back up' idea because so many people trash API. IMHO they are wrong. I think they equate finer gradations in the results chart and higher cost for the test kit with accuracy and that's just not true.
As for accuracy, none of them are really that good. And just because Salifert and Red Sea use finer scales or gradations, that doesn't make them more accurate. The test itself can still be wildly inaccurate and just shows the result on a finer graded chart. That isn't what accuracy is.
Our local club did a test kit test a few years back. More than 30 people brought their personal test kits to the meeting. Then we all did tests from the same sample of water and an additional sample was sent out to a professional lab for testing. The results did NOT show any test kit to be significantly better or worse than average, including API, Salifert and Red Sea. There were just a couple that were really off the mark but they were dip strip kits. The biggest take away from the test was that personal human skill at doing the tests was as important, if not more important, than which kit you used! There were users of Salifert and Red Sea that had bad results (high and low) just as often as the API users.
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