When testing your aquarium’s water, a single test for one parameter cannot yield difinitive results. Sure, the test can tell you something about what’s going on with the water. Unfortunately, the data from a single test cannot be considered valid until the test is repeated and a similar result is achieved. For example, if you test your water for ammonia one time and get an undetectable number, how can you be certain the aquarium is ammonia-free without trying it again? The answer is you really can’t. There is always a possibility for user error or the test to not work right for one reason or another. To remove this error and be more certain in a test kits results, try testing the water again to see if the original result can be duplicated. If the same number is achieved, or at the very least a data point that is close to the original, then you can rest assured that the test worked as it should. Too many times we trust in what our test kits say on the first time, and these results either lead to no action, or the aquarist taking some drastic measure to correct a wayward water parameter.