Liquid test kits are more accurate than strips, but only if you’re consistent about how you read them.
Always compare the sample tube against the color chart in the same lighting — ideally daylight or a daylight-balanced bulb, never under yellow incandescent light. Hold the tube directly against the white background provided in the kit, not against your countertop.
Shake reagent bottles for the full time stated on the label (usually 30 seconds), not a quick shake. Under-mixed reagent is the single biggest cause of inconsistent nitrate readings specifically.
If two readings taken minutes apart look different, don’t split the difference — re-test with fresh reagent drops and rule out a dirty test tube first.