ACTUALLY...
I used to sing the praises of the Salifert NO3 test kits, until my nitrate started going up, and going up, and I ran into problems controlling it with waterchanges... I like to keep my NO3 around 10, and that is a fairly easy number to read with the Salifert kit. But, my Sal kit started giving results around 25 and then between 25 and 50. So, I did a couple of water changes that barely made a dent. Then did a pretty big one that brought it down somewhat. I tested my RODI water because my membrane is over a year old, it read something like a couple ppm on the Sal test kit. I changed my sediment filter, I changed my DI resin. I tested with my BRS TDS meter - nothing, 0TDS. Retested after prefilter and DI cart change with the Sal kit - still a couple ppm. I made a quick and dirty standard up using ESV NO3 additive and tested that - way higher than it should have been. I pulled a nitrate standard from the lab - also way high. By trusting the Salifert results (my fault - I usually test a standard with each kit, but with this one I did not) I bottomed out my NO3.
So I ordered a HACH color disc NO3 kit. Super easy to use, Lab grade reagents, 2 minutes to test... turns out I had bottomed out my nitrate by putting trust in the Salifert NO3 kit - NO3 was 1ppm. I started having STN on my Montipora digitata!!! DIGITATA! Yikes! So, slowly brought it back up, and now I test 1x per week with the HACH kit. It's expensive, but the color disc is super easy to use with a very low chance of misinterpretation - even down low on the scale. It's spendy though. But, it is pretty accurate. Pinned my 10ppm standard (and not my quick and dirty one) perfectly, 3 times in a row.
I still like Salifert for ALK, and for Mg, but I will never trust their NO3 kit again. Have been using the ALK kit in the Mastertronic lately, and it works pretty well.
