I've tested my water for nitrates on each of my tanks once or twice in the last couple years. I stay on top of maintenance and I know what works, I go overboard to keep everything in the safe zone. I probably change more water than I need but my fish Don't seem to mind.
I used to monitor nitrates constantly, before I moved we had 30ppm out of the tap.
The API drop tests work much better than strips. At work im a sanitation team lead. We are responsible for cleaning stainless equipment in a food processing facility. I have to test all the chemicals before we use them and our test kits are remarkably similar to the API aquarium kits lol. I'm no chemist but I can tell you the drop test is far more accurate than using a conductivity meter, provided that you know how to titrate well.
+1 for cleaning your test equipment with deionized water. At the very least wash em out with Tap water aftwr each use.
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