Which one do you trust?

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I was calibrating my sybon refractometer and if i use the ultrapure fluid it gives me a reading .002 lower when i test with 1.026 calibration fluid from sybon.

So when i zero it and test cal fluid i get 1.024 and when i caibrate with 1.026 and read ultra pure i get 1.002.

I tend to trust 1.026 fluid more since its in the scale range we run tanks at.

 

[Reefing Madness]

 

[redfishbluefish]

When using a single calibration solution, you always will get the greatest accuracy by using a calibration solution closest to what you are measuring. You don't know if the calibration curve is perfectly linear. 53 mS/cm is the best calibration solution for aquarium use.