Both wet chemistry tests and spectrophotometer test are, in my humble opinion, equally reliable. The biggest variable with either testing methods is user technique (or lack thereof).
For the titration tests, Good Laboratory Practices need to be followed. The biggest error I see here is returning unused titrant to the mother bottle. Once you have finished the titration, and recorded the volume, squirt the rest of the syringe into the vial. Do not return it to the mother bottle. The second biggest error is simply following the instructions. And the last (for color changing titrations), it's the volume used once the color change occurs...not trying to match the color of the instruction card. Once the color change has occurred, note the volume on the syringe and add one more drop. If no further color change, you're done. Otherwise, continue with one drop until no further change.
For the spectrophotomer tests, what is critical is never, ever put the vial (cuvette) into the tester wet. Also, the vial needs to be squeaky clean before testing. Wipe it down with a soft cloth before putting into the tester. And finally, no bubbles in the vial...do not shake vigorously....swirl or slowly invert to mix reagents.
Just my two cents on testing!
Oh, and I use Red Sea for the troika....Alk, Calc and Mag, and use Hanna for phosphate, and API for nitrate.
