Test kits?

How do you know there not accurate?
Do you get different measurements form the same kit or same manufacturer?
Is there not enough resolution?

 

I primarily test all parameters with Salifert. More accurate testing is done at work (biophysical chemistry lab). 8)

 

The accuracy thing is determined IME a few ways. First when I can test the water w/ say 2 or 3 different "higher quality" tests that give roughly the same answer but the API will read higher or lower. When I test Ca w/ say my Tropic Marin(which is VERY PRECISE) I might get 418ppm but the API might say 360 or even 440ppm I have seen a HUGE difference.
Also I can use my experience and "knowledge" and deduce that if I am adding xppm of Ca a day and my Ca consumption isn't that heavy than my Ca wouldn't be that low.
The only way to get presice and ACCURATE readings is to use Hach LaMotte or Merck but these are nearly impossible to get your hands on if you are not a biologist or are in the testing field.

Good luck