API and Salifert Nitrate tests giving different resuts - Which is better

[ThickAsaBrick]

My last two posts laid out my recent frustration with Nitrate levels. I have trouble reading the API tests so I ordered the Salifert. It was one of the highest rated Nitrate test on a few sites I looked at. It showed up today.

My tanks have been at 40+ppm for multiple days seemingly regardless of what I do including an 80-90% change 2 days ago. My source water was reading around 30. Only my tap water has read much different. The tap water reads at 0.

I tested both of my tanks today when I got home with the Salifert test. My wife had already done a water change on both tanks. The API test says both tanks are about 30-40. The Salifert has one of my tanks at 5ppm and the other at 2.5ppm. A factor of ten difference is ridiculous but I'm not sure what to trust now.

My gut says the API test has to be faulty though it is only about 1 month old. SO I'm asking the smart people here. Is Salifert all it is cracked up to be? If not what do you think could be going on?

 

[layna]

I do 30% changes in my tank each week to try and reduce the nitrate, before a water change it seems hard to differentiate between 40ppm and 80ppm on the api test, a couple of hours after a water change it goes down to the darkest orange colour and im struggling to view this as a true reading for my nitrates too.

Soo TLR Im also interested to know others opinions as im unsure of the trueness of api's nitrate result