Can water testing kits ever be inaccurate?

Question

Even if you follow the instruction perfectly?

Answer 1

Water testing kits.... for fish tanks? There is a VERY tiny tiny possibility they are inaccurate. 99% of the time they are correct.

Answer 2

Yes they can actually. I would honestly recommend to not use the paper testing strips, as these are fairly inaccurate. The kind you get with a bottle dropper are more accurate, and there are the digital meter testers. If calibrated properly they should give you fairly accurate results. But for a cheaper method the drops will be accurate enough.

Answer 3

Kits?  Where you add chemicals to tubes of water- are far more accurate when used carefully then the test strips.  Test strips are still pretty accurate, but with a higher +/- margin of error.