Salifert is for sure a very suitable test to being a reference towards other methods/machines/tests, as the Salifert is exactly that sort of comparing test that Randy suggests. The Salifert hava an acid of 0.022N(that is not a secret, it is easy to calculate that from the included table). The only weak point is the color change, and as I have done around 1000 salifert tests last months I can tell you that you shall stop titrating at the absolut very first colour change, thus when it turns violet. If you measure the pH of that water, when turning to violet, you will find that is is very near around 4.2, thus the end titration point (approx) for HCO3 in marine-water. So when I for instance compare Hanna checker and Salifert I for sure rely more on Salifert